Pat
Excellent summary. I have only a few points to add. I must point out
that I am an RMAN novice, just getting brief spurts of time between other
people's priorities.
- If you use RMAN to back up to disk, I haven't figured an advantage to
backing archive logs up with RMAN. If anyone knows an advantage, I would
appreciate hearing it. Obviously if you are using RMAN to write to the MML,
it makes excellent sense to back up the archive logs, but writing to disk,
you just create an extra copy of your archive logs on disk, which eventually
gets copied to tape. RMAN will apply the archive logs, whether you've given
it charge of them or not. Since you are probably doing RMAN incremental
backups each day, you probably only need today's archive logs anyway.
- I appreciate your points on disaster recovery. This topic rarely seems
to come up with RMAN. We are into what might be termed "poor man's disaster
recovery". This isn't where you have a duplicate computer room in another
city (how do I apply to be the DBA at one of those facilities), but where
you take backup tapes offsite and your hardware vendor promises to find you
a replacement server somewhere to load your tapes into.
- The disaster recovery scenario our systems manager insists on is "your
server just burned to the floor, go get your backup tape from the offsite
vendor and go to a another location and get your system going." The key is
making sure that everything you need gets on that tape. I agree with you,
that when you rely on an MML, that is one more layer of uncertainty. How can
you make sure there isn't some key disk file the MML relies on, unless you
test the scenario.
- Someone on this list gave me the advice that it is easier to learn RMAN
by backing up to disk.
- A lot will depend on your site. I would expect that the larger the site,
the more benefit would be derived from and MML. And the more chance to get
payback from the training and learning.
- More disk space - when my system administrator realized by backing up to
disk he wouldn't need to learn how to interface Veritas to Oracle, he was
most enthusiastic about finding more disk space.
Dennis Williams
DBA
Lifetouch, Inc.
[EMAIL PROTECTED]
-----Original Message-----
Sent: Friday, May 31, 2002 4:05 PM
To: Multiple recipients of list ORACLE-L
I am currently wrestling with whether to implement 'rman disk backups' or
'rman tape backups'.
I have put together the following PRO's and CON's list so that I can weigh
my options.
I am putting this out to those on the list that are working with RMAN and
care to add to the points i have made.
It is open for discussion - I look forward to reading your responses.
PS : Either CC me on all question responses or I will get back to you on
Monday - I am currently in Oracle-L digest mode.
Thanks
TAPE
With this option rman directs the rman backup directly to tape.
PROs
- Disk Maintenance issues are not applicable ;
You do not have to be concerned about whether you have enough disk space for
your backups.
You do not have to setup, maintain and monitor daily cleanup jobs.
- Rman will be able to automate the recovery process for you ;
Rman knows where the backups reside (tape) and will recover them to disk -
as needed by the recovery process.
- Setting up a hourly remote copies of any new archive logs is easy - just
setup a tape archive copy.
CONs
- Recovery is slower (disk verse tape).
- When duplicating your database to a different server or in a true
disaster, where you have lost a server and you need to rebuild the instance
on a new server - You will have the added task (and time) of installing and
configuring the Media Management Layer (ie; Legato). Since your backups
reside on tape, the Media Management layer on the Oracle Server needs to be
installed and configured before you can talk with the backup server.
- You have to concern yourself about tape resource issues ;
A 'CROSSCHECK' or 'VERIFY' of your backup may keep the tape subsystem busy
loading, unloading and positioning tapes. If your tape subsystem is used
for other purposes other then your backup - then you could run into
resourcing issues around when and if you should be running these jobs.
- Also the submitting and scheduling of these tape backup jobs will probably
move out of the dba's control (cron) and into the tape management scheduling
group's control.
- With this option you must be use rman "Backups". Rman "Image copies" can
not be directed to tape.
DISK
With this option rman directs the rman backup directly to disk.
All of the Disk Pro's and Con's that I came up with were just the mirror
image of the Tape Con's and Pro's.
The catch with this option is you probably do not have enough disk space to
store all of your backups on disk, therefore you will need to put into place
a procedure that backs up your rman backup files to tape and then deletes
them from disk. Note that rman will still think that all of these backups
still reside on disk therefore it will become the dba's job to manage the
"backup-to-disk", "delete-from-disk" and the "recovery-from-tape" of these
rman backup datasets.
PROs
- Recovery is faster (disk verse tape) as long as the backup you want
resides on disk.
- When duplicating your database to a different server or in a true
disaster, where you have lost a server and you need to rebuild the instance
on a new server - You will not have the added task (and time) of installing
and configuring the Media Management Layer (ie; Legato Client). You would
use standard tape recovery procedures to recover your backups from tape -
then issue the rman recovery commands.
- You do not have to concern yourself about tape resource issues ;
You can schedule a 'CROSSCHECK' or 'VERIFY' of your backup without worrying
about impacting other outside resources.
- The dba is in total control of the tape backup scheduling.
- With this option you can use rman "Backups" or "Image copies".
CONs
- Disk Maintenance issues are applicable ;
You have to be concerned about whether you have enough disk space for your
backups.
You have to setup, maintain and monitor daily cleanup jobs.
- If the backup you want is not on disk Rman will not be able to automate
the recovery process for you ; Rman thinks that all the backups reside on
disk - he does not know that you have backed them up to tape and removed
them from the backup directory. Therefore it becomes the dba's job to
manage theses tasks.
- Setting up a manual hourly remote copy of any new archive logs is more
complex. This will give the dba more tape backups that he will have to
manage and keep track of.
_________________________
Patrick J. Howe
Oracle DBA
Illuminet. A Verisign Company.
4501 Intelco Loop SE
Olympia, WA 98507
Phone : 360.493.6284
Email : [EMAIL PROTECTED]
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