RE: redo log file setup with mirrored drives

2002-11-30 Thread Stephen Lee
> -Original Message-
> We hope by
> eliminating redo log multiplex, but with OS mirroring we 
> can speed up this loading process.

--

We deal with this by:

1.  Hardware mirroring of archives.
2.  Archives go to device on which no other I/O is present and, if there is
a difference in the speed of devices in the system (for example 7200 rpm
drives and 1 rpm drives), the archives get the faster drives.
3.  Alternating online redo between different devices, the theory being that
when a log switch occurs then the log being archived will be on a device
that is not being written to, so (we hope) the reads from that device will
be faster.

Even after making the archiving as fast as possible, you still might be
required to have a very large amount of online redo available in order to
handle the backlog built up during peak times.  We have found that archiving
is so much slower than online redo writing in a case like this, that we can
Oracle multiplex online redo to hardware RAID (redundant redundancy) and the
archiving will still be the slow point.

I wouldn't worry about the fault tolerance aspect of online redo mirroring,
since whatever would blow away both sides of a hardware or OS mirror would
also blow away both sides of Oracle multiplexing.  However, my experience
has shown that, as far as any debate on how one mirrors online redo the
point is moot.  My experience is that, in this scenario, the archiving is
what will snag things.
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Re: redo log file setup with mirrored drives

2002-11-29 Thread Yechiel Adar
Hello Guang

>From your note about weekly one day long import I think that you are dealing
with DW.
1) Am I correct?
2) Are there other updates to the database while the import is in progress?

Yechiel Adar
Mehish
- Original Message -
To: Multiple recipients of list ORACLE-L <[EMAIL PROTECTED]>
Sent: Wednesday, November 27, 2002 6:34 PM


> Hi:
>
> I am the original poster and thanks for all your inputs on this topic. Now
I
> know more about what "might" happen if something goes wrong. The main
> purpose of we thinking doing this was to gain some performance. We have a
> weekly schema imp process which takes about a day to finish. We hope by
> eliminating redo log multiplex, but with OS mirroring we can speed up this
> loading process. We are going to do some tests to see how much we would
> gain.
>
> BTW, our unix system admin is very good, I can trust him that we would
never
> delete any redo log files or any oracle files.
>
> So the only "practical danger" is that the redo file might get corrupted.
> This means we need to balance the "performance" vs "file curruption".
>
> Thanks again.
>
> Guang
>
>
>
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RE: redo log file setup with mirrored drives

2002-11-27 Thread Rachel Carmichael
I script and test as well. But sometimes you can't think of every
possible problem.

My point wasn't to have a contest of who had worse problems or who had
a problem that the other didn't.

merely that sometimes hardware mirroring is not the be-all/end-all
solution. 

We all could swap war stories for hours. But I need a beer before I
start that, that's thirsty work :)


--- Stephen Lee <[EMAIL PROTECTED]> wrote:
> > -Original Message-
> > have you NEVER accidentally, at 3AM, after having been woken from a
> > sound sleep to a crisis that needs to be fixed RIGHT NOW,  
> > made a typo?
> > 
> 
> Actually no.  But we usually script our actions and test the scripts
> prior
> to doing anything in production.  As a sys admin, I've restored
> enough
> casualties of the "rm -rf *" command to be rather careful about it
> myself.
> 
> > Um, I have.
> 
> I was wondering if anyone had.  But I could turn this around too and
> give an
> example of when duplexing the redos failed to save me.  One so-called
> patch
> that Compaq released for Tru64 actually caused disk writes to be
> unreliable
> (OH MY GOD!!).  And we wound up with a G.D. mess in spite of the
> redos being
> duplexed all nice and official.
> -- 
> Please see the official ORACLE-L FAQ: http://www.orafaq.com
> -- 
> Author: Stephen Lee
>   INET: [EMAIL PROTECTED]
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RE: redo log file setup with mirrored drives

2002-11-27 Thread Stephen Lee
> -Original Message-
> Sorry if you took offense at some attempted humor.
--
No offense taken here.  I've always worked in large environments where there
were multiple DBA's, sys admins, developers, and testers.  One cannot be
easily offended and survive in these environments.  You have your debates;
break a few chairs in the ensuing fight; then go out for lunch.  It's all a
nice break from the daily routine.
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RE: redo log file setup with mirrored drives

2002-11-27 Thread Jesse, Rich
Good point!  I'll take that one step further and suggest "select * from
v$instance" as that will also display the node that the DB is on.  Good to
know, especially if you have 3rd party apps that name the DBs the same.

Rich


Rich Jesse   System/Database Administrator
[EMAIL PROTECTED]  Quad/Tech International, Sussex, WI USA

> -Original Message-
> From: Rachel Carmichael [mailto:[EMAIL PROTECTED]]
> Sent: Wednesday, November 27, 2002 9:54 AM
> To: Multiple recipients of list ORACLE-L
> Subject: RE: redo log file setup with mirrored drives
> 

[snip]

> it. I've learned to ALWAYS do a "pwd" at the OS level and a "select *
> from v$database" when I am connected to a database.

[snip]
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RE: redo log file setup with mirrored drives

2002-11-27 Thread Rachel Carmichael
> I was amazed at the non-security that seems to be rampant out there,
> with mischievous people running around deleting files.  I kept
reading
> about it and thinking you've got to be kidding.

Steven,

have you NEVER accidentally, at 3AM, after having been woken from a
sound sleep to a crisis that needs to be fixed RIGHT NOW,  made a typo?

if not, wow, I'm in awe. All you need to do is forget which directory
you are in... and not include the path when do you an "rm". I've done
it. I've learned to ALWAYS do a "pwd" at the OS level and a "select *
from v$database" when I am connected to a database.

In any case, in another post you asked if anyone had ever lost a
database due to hardware mirroring.

Um, I have. Okay, we recovered the database via Data Unloader, but
essentially it was lost, because we couldn't open the database. The
current redo log and its hardware mirror failed. To this day, I don't
know why, there was a lot of finger pointing going on, including "you
mirrored it onto itself" and "you had both disks on the same controller
and it failed".

Regardless of WHY it happened, it happened. We could not switch the
current log, we could not open the database, we couldn't access
anything.

Tech support finally mentioned that there was this product that field
support had...

and two DAYS later I had a database again.

In this case, Oracle mirroring (no, we were not using multiplexed redo
logs) would possibly have saved us time, money and I might have had a
few less gray hairs.

Rachel

--- Stephen Lee <[EMAIL PROTECTED]> wrote:
> > -Original Message-
> > We do redo log file multiplexing to protect against fat 
> > fingers and other odd-ball stuff that have caused problems 
> > for an entire file system.  Call it an unreliable OS, poor SA 
> > (ok, maybe even DBA) practices
> 
> I do it because it's a CYA thing of doing it by the book.  I've
> listened to
> a lot of debates about database things and been amazed at the
> reasoning
> behind why people do what they do.  I've lost count of how many
> debates I've
> heard about extent sizes and numbers of extents, the majority of it
> pure
> superstition.  In the end, no matter how scientific or superstitious
> the
> reasoning, CYA trumps all.  So that's why I do it.  But, in fact,
> this whole
> thing about corrupt blocks is flawed reasoning.  If an OS cannot do
> disk
> writes in an absolutely reliable way, then the OS is unusable.  The
> bad
> writes will occur throughout the system.  This includes when your
> logs get
> archived and writes to data files.  Put those two together and what
> do you
> get?
> 
> Actually, there is one advantage to hardware mirroring of archives. 
> On
> Oracle duplexed archives, my experience is that it is inevitable that
> you
> will have one destination fill up while the other one doesn't.  In
> which
> case Oracle quietly quits using the one destination even after the
> files are
> removed during a backup.  I wrote a script to monitor when Oracle has
> stopped duplexing archived logs for those where we don't have
> hardware
> mirroring.
> 
> I was amazed at the non-security that seems to be rampant out there,
> with
> mischievous people running around deleting files.  I kept reading
> about it
> and thinking you've got to be kidding.
> -- 
> Please see the official ORACLE-L FAQ: http://www.orafaq.com
> -- 
> Author: Stephen Lee
>   INET: [EMAIL PROTECTED]
> 
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> 


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Re: redo log file setup with mirrored drives

2002-11-27 Thread Guang Mei
Hi:

I am the original poster and thanks for all your inputs on this topic. Now I 
know more about what "might" happen if something goes wrong. The main 
purpose of we thinking doing this was to gain some performance. We have a 
weekly schema imp process which takes about a day to finish. We hope by 
eliminating redo log multiplex, but with OS mirroring we can speed up this 
loading process. We are going to do some tests to see how much we would 
gain.

BTW, our unix system admin is very good, I can trust him that we would never 
delete any redo log files or any oracle files.

So the only "practical danger" is that the redo file might get corrupted. 
This means we need to balance the "performance" vs "file curruption".

Thanks again.

Guang



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RE: redo log file setup with mirrored drives

2002-11-27 Thread Stephen Lee
> -Original Message-
> have you NEVER accidentally, at 3AM, after having been woken from a
> sound sleep to a crisis that needs to be fixed RIGHT NOW,  
> made a typo?
> 

Actually no.  But we usually script our actions and test the scripts prior
to doing anything in production.  As a sys admin, I've restored enough
casualties of the "rm -rf *" command to be rather careful about it myself.

> Um, I have.

I was wondering if anyone had.  But I could turn this around too and give an
example of when duplexing the redos failed to save me.  One so-called patch
that Compaq released for Tru64 actually caused disk writes to be unreliable
(OH MY GOD!!).  And we wound up with a G.D. mess in spite of the redos being
duplexed all nice and official.
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RE: redo log file setup with mirrored drives

2002-11-27 Thread Jesse, Rich
Settle down.  ";)" means "joking".  Sheeesh.

And last I checked,  base 2 is still a natural integer, although I'm
obviously an idiot as I only took up to pre-calc.

Sorry if you took offense at some attempted humor.


Rich

Rich Jesse   System/Database Administrator
[EMAIL PROTECTED]  Quad/Tech International, Sussex, WI USA

> -Original Message-
> From: Stephen Lee [mailto:[EMAIL PROTECTED]]
> Sent: Tuesday, November 26, 2002 5:26 PM
> To: Multiple recipients of list ORACLE-L
> Subject: RE: redo log file setup with mirrored drives
> 
> > -Original Message-
> > Of course, you'll need Tom Kyte's binary conversion program 
> > here to execute this very weak proof:
> 
> Yeah, well this didn't come from Stephen Hawking.  And let's 
> not forget the
> part about "in the natural integers".  Homey didn't take a 
> bunch of 5000 and
> 6000 level math courses and come away entirely untrained.
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RE: redo log file setup with mirrored drives

2002-11-27 Thread Stephen Lee
> -Original Message-
> We do redo log file multiplexing to protect against fat 
> fingers and other odd-ball stuff that have caused problems 
> for an entire file system.  Call it an unreliable OS, poor SA 
> (ok, maybe even DBA) practices

I do it because it's a CYA thing of doing it by the book.  I've listened to
a lot of debates about database things and been amazed at the reasoning
behind why people do what they do.  I've lost count of how many debates I've
heard about extent sizes and numbers of extents, the majority of it pure
superstition.  In the end, no matter how scientific or superstitious the
reasoning, CYA trumps all.  So that's why I do it.  But, in fact, this whole
thing about corrupt blocks is flawed reasoning.  If an OS cannot do disk
writes in an absolutely reliable way, then the OS is unusable.  The bad
writes will occur throughout the system.  This includes when your logs get
archived and writes to data files.  Put those two together and what do you
get?

Actually, there is one advantage to hardware mirroring of archives.  On
Oracle duplexed archives, my experience is that it is inevitable that you
will have one destination fill up while the other one doesn't.  In which
case Oracle quietly quits using the one destination even after the files are
removed during a backup.  I wrote a script to monitor when Oracle has
stopped duplexing archived logs for those where we don't have hardware
mirroring.

I was amazed at the non-security that seems to be rampant out there, with
mischievous people running around deleting files.  I kept reading about it
and thinking you've got to be kidding.
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-- 
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Re: redo log file setup with mirrored drives

2002-11-27 Thread Igor Neyman
Amen to that!

Stephen,
It seems like you keep this discussion on just for the sake of discussion.
And also, it seems like you live in some kind of "ideal" world, where
hardware and software is 100% error-free and is 100% "bullet-proof" and
"fool-proof", and SAs, DBAs, developers, etc... never make a single mistake.
Good for you!
But most of us live in real world, where everything listed above is not
happening (yes, we, DBAs, make mistakes too).
So, we are TRYING to make our databases as reliable as possible (in
particular situation), using all the features provided with oracle db
including RedoLogs multiplexing (of course, using some common sense, and not
creating 20 members in one group).

Igor Neyman, OCP DBA
[EMAIL PROTECTED]



- Original Message -
To: "Multiple recipients of list ORACLE-L" <[EMAIL PROTECTED]>
Sent: Wednesday, November 27, 2002 8:43 AM


> >Now for those who are into this "worst scenario" thing let me ask you:
What
> >if I put your storage array between a 30HP air conditioning blower moter
and
> >a spot welder, and run a couple of paint shakers on top of the array to
> >boot.  What will your vaunted Oracle multiplexing do for you then?  Huh?
> >Well, smarty pants, I'm waiting!
>
> We do hardware mirroring to protect against controller and disk failures.
>
> We do redo log file multiplexing to protect against fat fingers and other
odd-ball stuff that have caused problems for an entire file system.  Call it
an unreliable OS, poor SA (ok, maybe even DBA) practices, whatever.  The
fact is that I've experienced it and I've been grateful to have the redo
logs multiplexed.  Each DBA can weigh the pros/cons and decide for
themselves.
>
> Given your scenario above, mirroring or multiplexing within the array
would both be useless.  The entire storage array would have to be mirrored.
But I don't rely on my multiplexing for this type of disaster.  The
multiplexing is for other issues I've encountered over the years.  I wish I
could maintain only 1 member redo log groups.  My OS is man-made and
occassionally has a bug.  Sometimes I'm brain-dead and make a stupid
mistake.  So I'm opting for all the protection I can get, because I don't
want to tell our company executives that their data is unrecoverable.
>
> Jay
>
> >>> [EMAIL PROTECTED] 11/26/02 09:49PM >>>
>
> -Original Message
> I believe the forgone conclusion you are talking about is that "mirroring
> outside of Oracle MAY result in data loss"  MAY is a very important word.
> The multiplexing of redo logs across multiple disks and controllers is a
> simple way protect your database from potential failure.
>
> Your position appears to be that hardware mirroring, software mirroring,
> RAID hardware, and the controllers feeding them all are infallible.
> 
>
> For those of you who are averse to the acquisition of knowledge through
> muscular debate, I trust you know where the DELETE button is.  For the
rest
> of you 
>
> As far as "MAY" goes, we can take that to any ridiculous extreme you wish
to
> take it.  The issue is NOT: "The multiplexing of redo logs across multiple
> disks and controllers".  The issue is HOW one does this.  Let's get this
> back to my original post.  I was responding to the implication that there
is
> some danger in using hardware mirroring such than one should not use it.
>
> As one who HAS ACTUALLY DONE BOTH and ACTUALLY USES BOTH and HAVE DONE SO
> FOR A LONG TIME (have you?) with both DATABASE and NON-DATABASE files, I
> felt it necessary to state that notwithstanding whatever armchair academia
> is floating around on the topic, I have NEVER experienced a loss with
> hardware mirroring;  And have never seen a  reason to imply that the
> practice has any inherent dangers.  Does that mean that a problem can
never
> occur?  Certainly not.  Have we ever had a controller or hard drive fail?
> Yes, indeed.  But, have we ever lost a database as a result?  Nope.
>
> Let me turn things around on you and look at Oracle multiplexing.  Has
> anyone ever lost a database who was doing Oracle multiplexing?  Sure.
Well
> gosh!  I thought this was supposed to keep this from happening.  Why
didn't
> it?
>
> The previous posts seemed to be totally preoccupied with this apparently
> ubiquitous phenomenon of corrupt blocks.  Let me ask you this: How often
> does it occur that you run your rman backup, and it detects bad blocks
that
> your OS missed or Oracle missed and failed to report?  I'm just curious to
> know how prevalent these things are.
>
> Another thing that was stated by the original response was that there was
> some performance benefit to Oracle doing the multiplexing -- that Oracle
> somehow "optimizes" the process.  In the case of software mirroring by the
> OS, this is a dubious statement.  In the case of hardware mirroring, the
> statement is patently false and is the main reason why one would use
> hardware mirro

RE: redo log file setup with mirrored drives

2002-11-27 Thread Jay Hostetter
>Now for those who are into this "worst scenario" thing let me ask you: What
>if I put your storage array between a 30HP air conditioning blower moter and
>a spot welder, and run a couple of paint shakers on top of the array to
>boot.  What will your vaunted Oracle multiplexing do for you then?  Huh?
>Well, smarty pants, I'm waiting!

We do hardware mirroring to protect against controller and disk failures.

We do redo log file multiplexing to protect against fat fingers and other odd-ball 
stuff that have caused problems for an entire file system.  Call it an unreliable OS, 
poor SA (ok, maybe even DBA) practices, whatever.  The fact is that I've experienced 
it and I've been grateful to have the redo logs multiplexed.  Each DBA can weigh the 
pros/cons and decide for themselves.

Given your scenario above, mirroring or multiplexing within the array would both be 
useless.  The entire storage array would have to be mirrored.  But I don't rely on my 
multiplexing for this type of disaster.  The multiplexing is for other issues I've 
encountered over the years.  I wish I could maintain only 1 member redo log groups.  
My OS is man-made and occassionally has a bug.  Sometimes I'm brain-dead and make a 
stupid mistake.  So I'm opting for all the protection I can get, because I don't want 
to tell our company executives that their data is unrecoverable.

Jay

>>> [EMAIL PROTECTED] 11/26/02 09:49PM >>>

-Original Message
I believe the forgone conclusion you are talking about is that "mirroring
outside of Oracle MAY result in data loss"  MAY is a very important word.
The multiplexing of redo logs across multiple disks and controllers is a
simple way protect your database from potential failure.

Your position appears to be that hardware mirroring, software mirroring,
RAID hardware, and the controllers feeding them all are infallible.


For those of you who are averse to the acquisition of knowledge through
muscular debate, I trust you know where the DELETE button is.  For the rest
of you 

As far as "MAY" goes, we can take that to any ridiculous extreme you wish to
take it.  The issue is NOT: "The multiplexing of redo logs across multiple
disks and controllers".  The issue is HOW one does this.  Let's get this
back to my original post.  I was responding to the implication that there is
some danger in using hardware mirroring such than one should not use it.

As one who HAS ACTUALLY DONE BOTH and ACTUALLY USES BOTH and HAVE DONE SO
FOR A LONG TIME (have you?) with both DATABASE and NON-DATABASE files, I
felt it necessary to state that notwithstanding whatever armchair academia
is floating around on the topic, I have NEVER experienced a loss with
hardware mirroring;  And have never seen a  reason to imply that the
practice has any inherent dangers.  Does that mean that a problem can never
occur?  Certainly not.  Have we ever had a controller or hard drive fail?
Yes, indeed.  But, have we ever lost a database as a result?  Nope.

Let me turn things around on you and look at Oracle multiplexing.  Has
anyone ever lost a database who was doing Oracle multiplexing?  Sure.  Well
gosh!  I thought this was supposed to keep this from happening.  Why didn't
it?

The previous posts seemed to be totally preoccupied with this apparently
ubiquitous phenomenon of corrupt blocks.  Let me ask you this: How often
does it occur that you run your rman backup, and it detects bad blocks that
your OS missed or Oracle missed and failed to report?  I'm just curious to
know how prevalent these things are.

Another thing that was stated by the original response was that there was
some performance benefit to Oracle doing the multiplexing -- that Oracle
somehow "optimizes" the process.  In the case of software mirroring by the
OS, this is a dubious statement.  In the case of hardware mirroring, the
statement is patently false and is the main reason why one would use
hardware mirroring -- because performance demands on the system require it.

Let's take this performance thing a little further.  As we have read in many
posts to the list, we even do such reckless and unthinkable things (at least
it was a few years ago) as allow storage arrays to cache our writes ... even
our redo writes (lions, tigers, and bears, oh my!) because performance
demands require it.  Now, you can peruse the database literature and find an
abundance of text on what a hideously EVIIL practice this is.  But we do
it anyway.  And, saints preserve us!  We don't have a landscape littered
with lost databases.

As one who has never lost a file of any kind to hardware or software
mirroring (well ... except for the early releases of Veritas on the Motorola
88K system where Veritas was a complete abortion and worse than nothing at
all) I am going to go with my own considerable experience on the subject.
If you wish to quote chapter and verse from this doc or that doc, that

RE: redo log file setup with mirrored drives

2002-11-26 Thread Stephen Lee

I suppose I should come clean on this deal and admit that we do indeed have
Oracle duplex the redo files.  The only time we would not do this is if some
user with sufficient bureaucratic power has some suckwad app and was
demanding that everything be done to bump up performance.  If it comes to
that, we'll do it and not lose any sleep over it.  Even though we have
Oracle duplexing, we still have had it happen that some storage array
maintenance person went in and managed to hose up both sides of the duplex.
Of course, this doesn't result in the loss of the database, but rather the
loss of some data.  But wasn't it fun debate.

What I found interesting was that nobody brought up what to do about the
archived logs -- how much mirroring is "enough" and how long to wait before
shoving them off onto tape.  Now, the loss of these babies can get you into
deep doodoo.  But, here again, we must sometimes make compromises for the
sake of a rotten application and overtaxed hardware.  At our shop here, we
are forced to rely on hardware mirroring of archives.  We have no choice.

You just try to get as many people to sign off on the setup as you can.

None of this changes the truth of anything I wrote.  I have found hardware
and software mirroring to be extremely reliable.  I have never lost a file
to it, and it has saved my butt many times.  At one place I worked, we
regularly tested yanking out power cords, I/O cables, storage array drawers,
anything we could think of, while the database and application were running
full blast.  It never failed once (except for early Veritas on Motorola 88K
which was a mess).
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RE: redo log file setup with mirrored drives

2002-11-26 Thread Stephen Lee

-Original Message
I believe the forgone conclusion you are talking about is that "mirroring
outside of Oracle MAY result in data loss"  MAY is a very important word.
The multiplexing of redo logs across multiple disks and controllers is a
simple way protect your database from potential failure.

Your position appears to be that hardware mirroring, software mirroring,
RAID hardware, and the controllers feeding them all are infallible.


For those of you who are averse to the acquisition of knowledge through
muscular debate, I trust you know where the DELETE button is.  For the rest
of you 

As far as "MAY" goes, we can take that to any ridiculous extreme you wish to
take it.  The issue is NOT: "The multiplexing of redo logs across multiple
disks and controllers".  The issue is HOW one does this.  Let's get this
back to my original post.  I was responding to the implication that there is
some danger in using hardware mirroring such than one should not use it.

As one who HAS ACTUALLY DONE BOTH and ACTUALLY USES BOTH and HAVE DONE SO
FOR A LONG TIME (have you?) with both DATABASE and NON-DATABASE files, I
felt it necessary to state that notwithstanding whatever armchair academia
is floating around on the topic, I have NEVER experienced a loss with
hardware mirroring;  And have never seen a  reason to imply that the
practice has any inherent dangers.  Does that mean that a problem can never
occur?  Certainly not.  Have we ever had a controller or hard drive fail?
Yes, indeed.  But, have we ever lost a database as a result?  Nope.

Let me turn things around on you and look at Oracle multiplexing.  Has
anyone ever lost a database who was doing Oracle multiplexing?  Sure.  Well
gosh!  I thought this was supposed to keep this from happening.  Why didn't
it?

The previous posts seemed to be totally preoccupied with this apparently
ubiquitous phenomenon of corrupt blocks.  Let me ask you this: How often
does it occur that you run your rman backup, and it detects bad blocks that
your OS missed or Oracle missed and failed to report?  I'm just curious to
know how prevalent these things are.

Another thing that was stated by the original response was that there was
some performance benefit to Oracle doing the multiplexing -- that Oracle
somehow "optimizes" the process.  In the case of software mirroring by the
OS, this is a dubious statement.  In the case of hardware mirroring, the
statement is patently false and is the main reason why one would use
hardware mirroring -- because performance demands on the system require it.

Let's take this performance thing a little further.  As we have read in many
posts to the list, we even do such reckless and unthinkable things (at least
it was a few years ago) as allow storage arrays to cache our writes ... even
our redo writes (lions, tigers, and bears, oh my!) because performance
demands require it.  Now, you can peruse the database literature and find an
abundance of text on what a hideously EVIIL practice this is.  But we do
it anyway.  And, saints preserve us!  We don't have a landscape littered
with lost databases.

As one who has never lost a file of any kind to hardware or software
mirroring (well ... except for the early releases of Veritas on the Motorola
88K system where Veritas was a complete abortion and worse than nothing at
all) I am going to go with my own considerable experience on the subject.
If you wish to quote chapter and verse from this doc or that doc, that's
great.  But I'm going to go with what I have actually seen tempered by any
tangible, objective, hard evidence I come across.

Now for those who are into this "worst scenario" thing let me ask you: What
if I put your storage array between a 30HP air conditioning blower moter and
a spot welder, and run a couple of paint shakers on top of the array to
boot.  What will your vaunted Oracle multiplexing do for you then?  Huh?
Well, smarty pants, I'm waiting!
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RE: redo log file setup with mirrored drives

2002-11-26 Thread Khedr, Waleed
I agree. And this is why Oracle has the capability to manage many redo log
members in the same group and many copies of the control file. It does not
offer the same for regular data files.

Regards,
Waleed

-Original Message-
Sent: Tuesday, November 26, 2002 6:05 PM
To: Multiple recipients of list ORACLE-L


"While all this is true, this is all based on the forgone conclusion that
mirroring outside Oracle will result in file loss.  It is that conclusion
with which I disagree."

I believe the forgone conclusion you are talking about is that "mirroring
outside of Oracle MAY result in data loss"  MAY is a very important word.
The multiplexing of redo logs across multiple disks and controllers is a
simple way protect your database from potential failure.  It is simply
irresponsible to dismiss it out of hand.  Sure you might cite performance
concerns, but for most databases in most enterprises redo log multiplexing
does not constitute a performance bottleneck.

Your position appears to be that hardware mirroring, software mirroring,
RAID hardware, and the controllers feeding them all are infallible.
Multiplexing redo logs is simply a form of insurance, and should be
considered a default element of Oracle database design.

Steve

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RE: redo log file setup with mirrored drives

2002-11-26 Thread Steve McClure
"While all this is true, this is all based on the forgone conclusion that
mirroring outside Oracle will result in file loss.  It is that conclusion
with which I disagree."

I believe the forgone conclusion you are talking about is that "mirroring
outside of Oracle MAY result in data loss"  MAY is a very important word.
The multiplexing of redo logs across multiple disks and controllers is a
simple way protect your database from potential failure.  It is simply
irresponsible to dismiss it out of hand.  Sure you might cite performance
concerns, but for most databases in most enterprises redo log multiplexing
does not constitute a performance bottleneck.

Your position appears to be that hardware mirroring, software mirroring,
RAID hardware, and the controllers feeding them all are infallible.
Multiplexing redo logs is simply a form of insurance, and should be
considered a default element of Oracle database design.

Steve

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RE: redo log file setup with mirrored drives

2002-11-26 Thread Stephen Lee


> -Original Message-
> Of course, you'll need Tom Kyte's binary conversion program 
> here to execute this very weak proof:

Yeah, well this didn't come from Stephen Hawking.  And let's not forget the
part about "in the natural integers".  Homey didn't take a bunch of 5000 and
6000 level math courses and come away entirely untrained.
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RE: redo log file setup with mirrored drives

2002-11-26 Thread Jesse, Rich
Theory: 2 + 2 = 15

SELECT 2 + 2 FROM DUAL;
SELECT 1+1 + 1+1 FROM DUAL;
SELECT TO_CHAR(1)||TO_CHAR(1)||TO_CHAR(1)||TO_CHAR(1) FROM DUAL;
SELECT to_dec(TO_CHAR(1)||TO_CHAR(1)||TO_CHAR(1)||TO_CHAR(1),2) FROM DUAL;

Of course, you'll need Tom Kyte's binary conversion program here to execute
this very weak proof:

http://govt.oracle.com/~tkyte/hexdec/hexdec.sql

;)

Rich
Beer-free for almost 17 hours.


Rich Jesse   System/Database Administrator
[EMAIL PROTECTED]  Quad/Tech International, Sussex, WI USA

> -Original Message-
> From: Fink, Dan [mailto:[EMAIL PROTECTED]]
> Sent: Tuesday, November 26, 2002 2:25 PM
> To: Multiple recipients of list ORACLE-L
> Subject: RE: redo log file setup with mirrored drives
> 
> 
> Stephen,
>   Nothing is gained by personal attacks in this forum. 
> This forum is
> intended to be a learning experience for all (myself 
> included). I suggest
> that you review the archived list and examine the quality of 
> posts by Kirti,
> Jared, et.al. They speak for themselves.
> 
>   BTW, 2 + 2 does equal 15 for very large values of 2 and 
> very small
> values of 15. ;)
> Dan Fink
> 
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RE: redo log file setup with mirrored drives

2002-11-26 Thread Stephen Lee


> -Original Message-
> Stephen,
>   Nothing is gained by personal attacks in this forum. 

Please enlighten me.  Exactly what personal attack was made?
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RE: redo log file setup with mirrored drives

2002-11-26 Thread Brian Haas
On Tue, 2002-11-26 at 10:50, Stephen Lee wrote:
 
 And from another post ...
> > Because my OS/hardware IS reliable a corrupted 
> > log file that is mirrored outside of Oracle will be corrupt - 
> > the original is corrupt, so is the mirror.
> 
> In one sentence you have claimed that your "OS/hardware IS reliable" and
> talk about it corrupting log files.  Are we having a problem with the
> definition of "reliable" here?
> 

Hmmm..I don't think the original poster is saying the OS corrupted the
log file. The post is merely mentioning that if a non-oracle mirrored
redo log was to become corrupted(by any means) the mirror copy will be
corrupted as well, but an Oracle multiplexed copy might not be.

> This goes back to an old post of using NT versus Unix.  If you recall, my
> reply was that security on NT was so bad, that it is not a good choice.
> This stems primarily from the fact that NT is essentially a single-user OS,
> built around the administrator, with some multi-user extensions kludged on
> to support non-administrator pseudo-users.

> Going back to the original post on this topic: There was nothing that
> suggested they were in a pathological environment.  For what it's worth,
> when we had databases on NT, we followed a strict directory naming routine
> and made it clear to the NT admins that any directory with certain names
> were not to be touched.  If anything needed to be done with those
> directories, they were to page us.

Last time I checked most SA's have root access. Therefore they can
delete(accidentally or otherwise) any of your Oracle files. Granted, Joe
Schmoe user won't be able to do this, but how often is user Joe Schmoe
logging on to an NT Oracle box? So I would say your NT point is moot.
The same security precautions from admins is needed in a Unix
environment as well.

If you read the original post again, the poster asked if there was any
"danger" to just using OS mirroring. I think the potential dangers were
addressed and the question was answered. I don't think anyone was
questioning the reliability of OS mirroring, but as an administrator, I
think it is in my best interest to take worst case scenarios into
account. 

> Concluding remarks:
> While the scenarios of gloom and doom that have been painted by some seem to
> be credible, I've have yet to witness, in my years of personal experience as
> a sys admin and a database admin the unreliability that some claim to exist.
> That being the case, I must go with the arrangement that I think offers
> fault tolerance with the best performance.

As with any database installation the old "it depends" works every time.
There are best practices, but each situation is different and has
different requirements for reliability, uptime,security, etc. If just
using OS mirroring is the best choice for your installation that's
great, but it might not be the best choice for all. 


-Brian

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RE: redo log file setup with mirrored drives

2002-11-26 Thread Jesse, Rich
Precisely why I name all Oracle files with ".dbf" extension.  Who ever
thought naming a redo log with ".log" was a good idea???  With all DB files
the same, it's a simple rule:  Don't touch .dbf files.  No confusion there.
If you need to mess with them (backups, etc), write and test a script.  Try
to prevent yourself from making a mistake.

"If at first you don't succeed, you had better be in test."

My $.02,
Rich


Rich Jesse   System/Database Administrator
[EMAIL PROTECTED]  Quad/Tech International, Sussex, WI USA

> -Original Message-
> From: Fink, Dan [mailto:[EMAIL PROTECTED]]
> Sent: Tuesday, November 26, 2002 10:05 AM
> To: Multiple recipients of list ORACLE-L
> Subject: RE: redo log file setup with mirrored drives
> 

[snip] 

> not protect against the accidental deletion of the file. I 
> have had to deal
> with situations where people deleted the redo logs (disk 
> space at 90%, let's
> clear out the log files...). Another copy on another device 

[snip]
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RE: redo log file setup with mirrored drives

2002-11-26 Thread Fink, Dan
Stephen,
Nothing is gained by personal attacks in this forum. This forum is
intended to be a learning experience for all (myself included). I suggest
that you review the archived list and examine the quality of posts by Kirti,
Jared, et.al. They speak for themselves.

BTW, 2 + 2 does equal 15 for very large values of 2 and very small
values of 15. ;)
Dan Fink

-Original Message-
Sent: Tuesday, November 26, 2002 11:50 AM
To: Multiple recipients of list ORACLE-L



I was going to let the differences of opinion stand, but I suppose this
requires an answer.

> -Original Message-
> 
> Redo and archived redo logs are the most important files in 
> the database. 
> Lose a datafile? You can still recover the database.
> Lose all controlfiles? They can be recreated.
> Lose a single redo entry? Your recovery is terminated. Yes, there are
> unsupported methods to bypass this condition, but they are 
> kludges and may
> be very, very expensive.

While all this is true, this is all based on the forgone conclusion that
mirroring outside Oracle will result in file loss.  It is that conclusion
with which I disagree.

> So, why do I still multiplex my redo logs (even on my 'test' 
> Win2k databases
> at home)? O/S level mirroring protects against some failures, 
> but it does
> not protect against the accidental deletion of the file. I 
> have had to deal
> with situations where people deleted the redo logs (disk 
> space at 90%, let's
> clear out the log files...). Another copy on another device 
> (usually with a
> separate controller), saved the database.

In your case, your problems are not related to mirroring technique. Yours
deal with how best to handle pathological situations, shops with
non-existent security, and incompetent administration.  That's certainly a
valid topic for discussion, but isn't the topic of my discussion.

> 
> Considering the small size of the redo logs and their 
> critical importance to
> the database, I'll both multiplex (oracle) and mirror (o/s).
> 

The redo logs on our production databases are from 100 Mb to 1 Gb.  Hence,
the issue is not just one of how bullet proof things can be made, but one of
performance too.

> 
> "1.  This is pure speculation."
> Kirti is one of the many people on this list who has shown 
> time and time
> again that he does not engage in "pure speculation".

In this case he was.  He was speculating about how OS's and RAIDing hardware
go about their business and how reliably they do it.  He was speculating
that, if one does not mirror via Oracle, then one will get bad redo files.

As is commonly the case, there is some tendency to assign human qualities to
computer things; things such as "knowing" about something; and the capacity
to reason and make decisions; and the ability to have a moment of
inattention when it just "forgot" to do something right.  Computers (other
than ones named HAL) don't work this way.  The original question was posed
by someone who we can safely assume is NOT running a database on some
crapola OS with rickety, unreliable, and outdated hardware (in which case, I
don't think ANY kind of mirroring will help).  If this discussion were ten
years ago, you might have a point.  But this isn't ten years ago.

> While a skeptical
> attitude is good and helps you develop, I tend to accept 
> Kirti's posts (and
> Cary's, Tim's, Jared's, Robert's, and others on the 10 list) 
> at face value
> until I put together a test case and can prove it or disprove it.

It sounds to me like you don't intend to do either.

If Stephen Hawking attempted to tell me that, in the natural integers, 2 + 2
= 15, I would know immediately that what he was telling me was incorrect.  I
have no knowledge of Kirti's expertise in computer operating systems and
hardware.  But I do know the facts.  In my past life as a Unix sys admin, I
worked with OS's and RAID hardware enough to know that file maintenance
isn't the roll of the dice that you are making it out to be.  The suggestion
that an EMC array can't be trusted to properly mirror files raises the
question: Why did you spend a million bucks on it then?

And from another post ...
> Because my OS/hardware IS reliable a corrupted 
> log file that is mirrored outside of Oracle will be corrupt - 
> the original is corrupt, so is the mirror.

In one sentence you have claimed that your "OS/hardware IS reliable" and
talk about it corrupting log files.  Are we having a problem with the
definition of "reliable" here?

And from another post
> Ditto.
> 
> The biggest problem with non-Oracle-mirrored  redo log is
> a personnel issue.
> 
> Take it from someone who's experienced a SA deleting all
> files from a 500 Gig DW during the middle of the day.

This goes back to an old post of using NT versus Unix.  If you recall, my
reply was that security on NT was so bad, that it is not a good choice.
This stems primarily from the fact that NT is essentially a single-user OS,
built around the administrator, wit

RE: redo log file setup with mirrored drives

2002-11-26 Thread Stephen Lee

I was going to let the differences of opinion stand, but I suppose this
requires an answer.

> -Original Message-
> 
> Redo and archived redo logs are the most important files in 
> the database. 
> Lose a datafile? You can still recover the database.
> Lose all controlfiles? They can be recreated.
> Lose a single redo entry? Your recovery is terminated. Yes, there are
> unsupported methods to bypass this condition, but they are 
> kludges and may
> be very, very expensive.

While all this is true, this is all based on the forgone conclusion that
mirroring outside Oracle will result in file loss.  It is that conclusion
with which I disagree.

> So, why do I still multiplex my redo logs (even on my 'test' 
> Win2k databases
> at home)? O/S level mirroring protects against some failures, 
> but it does
> not protect against the accidental deletion of the file. I 
> have had to deal
> with situations where people deleted the redo logs (disk 
> space at 90%, let's
> clear out the log files...). Another copy on another device 
> (usually with a
> separate controller), saved the database.

In your case, your problems are not related to mirroring technique. Yours
deal with how best to handle pathological situations, shops with
non-existent security, and incompetent administration.  That's certainly a
valid topic for discussion, but isn't the topic of my discussion.

> 
> Considering the small size of the redo logs and their 
> critical importance to
> the database, I'll both multiplex (oracle) and mirror (o/s).
> 

The redo logs on our production databases are from 100 Mb to 1 Gb.  Hence,
the issue is not just one of how bullet proof things can be made, but one of
performance too.

> 
> "1.  This is pure speculation."
> Kirti is one of the many people on this list who has shown 
> time and time
> again that he does not engage in "pure speculation".

In this case he was.  He was speculating about how OS's and RAIDing hardware
go about their business and how reliably they do it.  He was speculating
that, if one does not mirror via Oracle, then one will get bad redo files.

As is commonly the case, there is some tendency to assign human qualities to
computer things; things such as "knowing" about something; and the capacity
to reason and make decisions; and the ability to have a moment of
inattention when it just "forgot" to do something right.  Computers (other
than ones named HAL) don't work this way.  The original question was posed
by someone who we can safely assume is NOT running a database on some
crapola OS with rickety, unreliable, and outdated hardware (in which case, I
don't think ANY kind of mirroring will help).  If this discussion were ten
years ago, you might have a point.  But this isn't ten years ago.

> While a skeptical
> attitude is good and helps you develop, I tend to accept 
> Kirti's posts (and
> Cary's, Tim's, Jared's, Robert's, and others on the 10 list) 
> at face value
> until I put together a test case and can prove it or disprove it.

It sounds to me like you don't intend to do either.

If Stephen Hawking attempted to tell me that, in the natural integers, 2 + 2
= 15, I would know immediately that what he was telling me was incorrect.  I
have no knowledge of Kirti's expertise in computer operating systems and
hardware.  But I do know the facts.  In my past life as a Unix sys admin, I
worked with OS's and RAID hardware enough to know that file maintenance
isn't the roll of the dice that you are making it out to be.  The suggestion
that an EMC array can't be trusted to properly mirror files raises the
question: Why did you spend a million bucks on it then?

And from another post ...
> Because my OS/hardware IS reliable a corrupted 
> log file that is mirrored outside of Oracle will be corrupt - 
> the original is corrupt, so is the mirror.

In one sentence you have claimed that your "OS/hardware IS reliable" and
talk about it corrupting log files.  Are we having a problem with the
definition of "reliable" here?

And from another post
> Ditto.
> 
> The biggest problem with non-Oracle-mirrored  redo log is
> a personnel issue.
> 
> Take it from someone who's experienced a SA deleting all
> files from a 500 Gig DW during the middle of the day.

This goes back to an old post of using NT versus Unix.  If you recall, my
reply was that security on NT was so bad, that it is not a good choice.
This stems primarily from the fact that NT is essentially a single-user OS,
built around the administrator, with some multi-user extensions kludged on
to support non-administrator pseudo-users.

Going back to the original post on this topic: There was nothing that
suggested they were in a pathological environment.  For what it's worth,
when we had databases on NT, we followed a strict directory naming routine
and made it clear to the NT admins that any directory with certain names
were not to be touched.  If anything needed to be done with those
directories, they were to page us.

Concluding rem

RE: redo log file setup with mirrored drives

2002-11-26 Thread Jared . Still
Ditto.

The biggest problem with non-Oracle-mirrored  redo log is
a personnel issue.

Take it from someone who's experienced a SA deleting all
files from a 500 Gig DW during the middle of the day.

Jared






"Fink, Dan" <[EMAIL PROTECTED]>
Sent by: [EMAIL PROTECTED]
 11/26/2002 08:04 AM
 Please respond to ORACLE-L

 
To: Multiple recipients of list ORACLE-L <[EMAIL PROTECTED]>
cc: 
    Subject:    RE: redo log file setup with mirrored drives


"Pending further evidence to the contrary, I'll take mirroring external to
Oracle as the better choice."

Redo and archived redo logs are the most important files in the database. 
Lose a datafile? You can still recover the database.
Lose all controlfiles? They can be recreated.
Lose a single redo entry? Your recovery is terminated. Yes, there are
unsupported methods to bypass this condition, but they are kludges and may
be very, very expensive.

So, why do I still multiplex my redo logs (even on my 'test' Win2k 
databases
at home)? O/S level mirroring protects against some failures, but it does
not protect against the accidental deletion of the file. I have had to 
deal
with situations where people deleted the redo logs (disk space at 90%, 
let's
clear out the log files...). Another copy on another device (usually with 
a
separate controller), saved the database. 

Considering the small size of the redo logs and their critical importance 
to
the database, I'll both multiplex (oracle) and mirror (o/s).


"1.  This is pure speculation."
Kirti is one of the many people on this list who has shown time and time
again that he does not engage in "pure speculation". While a skeptical
attitude is good and helps you develop, I tend to accept Kirti's posts 
(and
Cary's, Tim's, Jared's, Robert's, and others on the 10 list) at face value
until I put together a test case and can prove it or disprove it.

Dan Fink
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RE: redo log file setup with mirrored drives

2002-11-26 Thread VIVEK_SHARMA

Also stand by that "corrupted write will be restricted to just the affected member"
Hence one can simply overwrite the BAD (Corrupted) member with the Good one


-Original Message-
Sent: Tuesday, November 26, 2002 9:40 PM
To: Multiple recipients of list ORACLE-L


Sure... 

What I posted came from my discussions with others and from various resources on 
Metalink and from Oracle Training Classes. Note #45042.1 titled Archiver Best 
Practices summarizes it all. 

Agreed, that RAID and disk technologies have improved over the years, however, I would 
still continue using multiple redo log members on any OS. Redo log files serve 
different purpose in an Oracle database, and so should be treated differently. 

- Kirti
 

-Original Message-
Sent: Tuesday, November 26, 2002 9:24 AM
To: Multiple recipients of list ORACLE-L



If I may offer another view 

> -Original Message-
> Having multiple redo log members has its advantages. The 
> archiver process 'knows' these multiple members and it will 
> optimize the archiving process,

Is there any supporting documentation about this "optimizing"?  Are you
saying that the makers of hardware-based and software-based RAID have not
"optimized" their RAIDing?  If I were a betting man, I would bet that a
hardware device can do mirrored writes faster than Oracle.

> but it does not know about 
> the mirrored copies of these logs.

Know?  What does it need to "know"?  Mirroring is mirroring.  A mirrored
copy either exists, or it doesn't.  "Knowing" about it has no effect on the
existence of the copy.  Computer operations aren't based on faith (although
there are many times we are tempted to question that).

> The other important thing 
> to know is that Oracle issues a separate write for these log 
> members

And this improves performance?

> and in an unlikely event a corrupted write will be 
> restricted to just the affected member.  Such corruption will 
> affect all the mirrored copies. 

Two things:
1.  This is pure speculation.
2.  If your OS can't do reliable disk writes, then it's time to get a new
OS.  A database consists of more than just redo logs.  It also has pesky
little things like data files.  Should we have Oracle mirror those too
rather than rely on RAIDing for fault tolerance?  Why would we expect the OS
to reliably write data files and detect hardware errors when it can't
reliably maintain redo logs?

Pending further evidence to the contrary, I'll take mirroring external to
Oracle as the better choice.
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RE: redo log file setup with mirrored drives

2002-11-26 Thread Deshpande, Kirti
Sure... 

What I posted came from my discussions with others and from various resources on 
Metalink and from Oracle Training Classes. Note #45042.1 titled Archiver Best 
Practices summarizes it all. 

Agreed, that RAID and disk technologies have improved over the years, however, I would 
still continue using multiple redo log members on any OS. Redo log files serve 
different purpose in an Oracle database, and so should be treated differently. 

- Kirti
 

-Original Message-
Sent: Tuesday, November 26, 2002 9:24 AM
To: Multiple recipients of list ORACLE-L



If I may offer another view 

> -Original Message-
> Having multiple redo log members has its advantages. The 
> archiver process 'knows' these multiple members and it will 
> optimize the archiving process,

Is there any supporting documentation about this "optimizing"?  Are you
saying that the makers of hardware-based and software-based RAID have not
"optimized" their RAIDing?  If I were a betting man, I would bet that a
hardware device can do mirrored writes faster than Oracle.

> but it does not know about 
> the mirrored copies of these logs.

Know?  What does it need to "know"?  Mirroring is mirroring.  A mirrored
copy either exists, or it doesn't.  "Knowing" about it has no effect on the
existence of the copy.  Computer operations aren't based on faith (although
there are many times we are tempted to question that).

> The other important thing 
> to know is that Oracle issues a separate write for these log 
> members

And this improves performance?

> and in an unlikely event a corrupted write will be 
> restricted to just the affected member.  Such corruption will 
> affect all the mirrored copies. 

Two things:
1.  This is pure speculation.
2.  If your OS can't do reliable disk writes, then it's time to get a new
OS.  A database consists of more than just redo logs.  It also has pesky
little things like data files.  Should we have Oracle mirror those too
rather than rely on RAIDing for fault tolerance?  Why would we expect the OS
to reliably write data files and detect hardware errors when it can't
reliably maintain redo logs?

Pending further evidence to the contrary, I'll take mirroring external to
Oracle as the better choice.
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RE: redo log file setup with mirrored drives

2002-11-26 Thread Jay Hostetter
  Addressing the corruption issue, Kirti's statement is not speculation.  Because my 
OS/hardware IS reliable a corrupted log file that is mirrored outside of Oracle will 
be corrupt - the original is corrupt, so is the mirror.  If I mirror my log files 
using Oracle, logfile A may be corrupt, but log file B may NOT be corrupt, depending 
on what caused the corruption (if it is some Oracle bug, then you're out of luck 
either way). 
  We had a case where all files that were open on a particular file system became 
corrupt.  The cause was related to a bug in the cluster software during a system 
crash.  This file system was RAID 0+1 - which meant that my file was "safe", 
corruption and all.  Fortunately, I had Oracle mirroring the redo log on another file 
system which was unaffected by the crash.

Jay

>>> [EMAIL PROTECTED] 11/26/02 10:23AM >>>

If I may offer another view 

> -Original Message-
> Having multiple redo log members has its advantages. The 
> archiver process 'knows' these multiple members and it will 
> optimize the archiving process,

Is there any supporting documentation about this "optimizing"?  Are you
saying that the makers of hardware-based and software-based RAID have not
"optimized" their RAIDing?  If I were a betting man, I would bet that a
hardware device can do mirrored writes faster than Oracle.

> but it does not know about 
> the mirrored copies of these logs.

Know?  What does it need to "know"?  Mirroring is mirroring.  A mirrored
copy either exists, or it doesn't.  "Knowing" about it has no effect on the
existence of the copy.  Computer operations aren't based on faith (although
there are many times we are tempted to question that).

> The other important thing 
> to know is that Oracle issues a separate write for these log 
> members

And this improves performance?

> and in an unlikely event a corrupted write will be 
> restricted to just the affected member.  Such corruption will 
> affect all the mirrored copies. 

Two things:
1.  This is pure speculation.
2.  If your OS can't do reliable disk writes, then it's time to get a new
OS.  A database consists of more than just redo logs.  It also has pesky
little things like data files.  Should we have Oracle mirror those too
rather than rely on RAIDing for fault tolerance?  Why would we expect the OS
to reliably write data files and detect hardware errors when it can't
reliably maintain redo logs?

Pending further evidence to the contrary, I'll take mirroring external to
Oracle as the better choice.




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RE: redo log file setup with mirrored drives

2002-11-26 Thread Fink, Dan
"Pending further evidence to the contrary, I'll take mirroring external to
Oracle as the better choice."

Redo and archived redo logs are the most important files in the database. 
Lose a datafile? You can still recover the database.
Lose all controlfiles? They can be recreated.
Lose a single redo entry? Your recovery is terminated. Yes, there are
unsupported methods to bypass this condition, but they are kludges and may
be very, very expensive.

So, why do I still multiplex my redo logs (even on my 'test' Win2k databases
at home)? O/S level mirroring protects against some failures, but it does
not protect against the accidental deletion of the file. I have had to deal
with situations where people deleted the redo logs (disk space at 90%, let's
clear out the log files...). Another copy on another device (usually with a
separate controller), saved the database. 

Considering the small size of the redo logs and their critical importance to
the database, I'll both multiplex (oracle) and mirror (o/s).


"1.  This is pure speculation."
Kirti is one of the many people on this list who has shown time and time
again that he does not engage in "pure speculation". While a skeptical
attitude is good and helps you develop, I tend to accept Kirti's posts (and
Cary's, Tim's, Jared's, Robert's, and others on the 10 list) at face value
until I put together a test case and can prove it or disprove it.

Dan Fink
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RE: redo log file setup with mirrored drives

2002-11-26 Thread Stephen Lee

If I may offer another view 

> -Original Message-
> Having multiple redo log members has its advantages. The 
> archiver process 'knows' these multiple members and it will 
> optimize the archiving process,

Is there any supporting documentation about this "optimizing"?  Are you
saying that the makers of hardware-based and software-based RAID have not
"optimized" their RAIDing?  If I were a betting man, I would bet that a
hardware device can do mirrored writes faster than Oracle.

> but it does not know about 
> the mirrored copies of these logs.

Know?  What does it need to "know"?  Mirroring is mirroring.  A mirrored
copy either exists, or it doesn't.  "Knowing" about it has no effect on the
existence of the copy.  Computer operations aren't based on faith (although
there are many times we are tempted to question that).

> The other important thing 
> to know is that Oracle issues a separate write for these log 
> members

And this improves performance?

> and in an unlikely event a corrupted write will be 
> restricted to just the affected member.  Such corruption will 
> affect all the mirrored copies. 

Two things:
1.  This is pure speculation.
2.  If your OS can't do reliable disk writes, then it's time to get a new
OS.  A database consists of more than just redo logs.  It also has pesky
little things like data files.  Should we have Oracle mirror those too
rather than rely on RAIDing for fault tolerance?  Why would we expect the OS
to reliably write data files and detect hardware errors when it can't
reliably maintain redo logs?

Pending further evidence to the contrary, I'll take mirroring external to
Oracle as the better choice.
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RE: redo log file setup with mirrored drives

2002-11-25 Thread Deshpande, Kirti
Having multiple redo log members has its advantages. The archiver process 'knows' 
these multiple members and it will optimize the archiving process, but it does not 
know about the mirrored copies of these logs. The other important thing to know is 
that Oracle issues a separate write for these log members and in an unlikely event a 
corrupted write will be restricted to just the affected member. Such corruption will 
affect all the mirrored copies. 

- Kirti

-Original Message-
Sent: Monday, November 25, 2002 7:54 PM
To: Multiple recipients of list ORACLE-L


Hi:

We have oracle 8173 running on Sun Solaris box. The current redo files are:

/oracle/oradata/RPT1/redo101.log
/oracle/oradata/RPT1/redo201.log
/oracle/oradata/RPT1/redo301.log
/oracle/u01/oradata/RPT1/redo102.log
/oracle/u01/oradata/RPT1/redo202.log
/oracle/u01/oradata/RPT1/redo302.log

The members of the same group are in different disks. Now we are going to 
set up new disks soon and they are mirrored drives (the sys admin told me). 
Because they are already mirrored, can I just create ONE redo member for 
each group (instead of two) in the new setup? Is there any "danger" to do 
that?

TIA.

Guang




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redo log file setup with mirrored drives

2002-11-25 Thread Guang Mei
Hi:

We have oracle 8173 running on Sun Solaris box. The current redo files are:

/oracle/oradata/RPT1/redo101.log
/oracle/oradata/RPT1/redo201.log
/oracle/oradata/RPT1/redo301.log
/oracle/u01/oradata/RPT1/redo102.log
/oracle/u01/oradata/RPT1/redo202.log
/oracle/u01/oradata/RPT1/redo302.log

The members of the same group are in different disks. Now we are going to 
set up new disks soon and they are mirrored drives (the sys admin told me). 
Because they are already mirrored, can I just create ONE redo member for 
each group (instead of two) in the new setup? Is there any "danger" to do 
that?

TIA.

Guang




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