1. depends on the stripe width, data may be on one or many drives, parity
will always get written to all.
2. I believe your performance will be better; you have 6 drives for data,
and 4 for archive/redo. That equates to 12 drives over the previous 8.
However, you were using all eight for everything.
I don't believe there is any purpose to mirror the four drives, I like to
use Raid 0 or single drives for redo, and just do multiple members and
archive destinations. Redo/Archive is high write activity, Raid 1 takes a
small hit on write, and only benefits read performance. You can get the
same redundancy using duplex destination and multiple members.
Having redo logs and archive logs separate will prove to be beneficial.
All and all, I think you will come up with a better configuration
performance-wise.
Make sure the A1000 has the 80Mb cache, and has the latest firmware, as it
there are a lot of buggy A1000's out there that cause corruption if they are
saturated.
"Do not criticize someone until you walked a mile in their shoes, that way
when you criticize them, you are a mile a way and have their shoes."
Christopher R. Spence
Oracle DBA
Phone: (978) 322-5744
Fax: (707) 885-2275
Fuelspot
73 Princeton Street
North, Chelmsford 01863
-----Original Message-----
Sent: Friday, September 21, 2001 10:15 AM
To: Multiple recipients of list ORACLE-L
Hi,
I'm encuntering a relatively high iowait percentage
when my hot backups are running. The platform is Sun
(E420 2cpu running SunOS 5.7) with an A1000 disk array
(8 9Gb drives, hardware Raid-5). The array is one
volume and all DB components (redo, archive, data,
index, system, etc.) are on the same volume except for
the binaries. The database is not large, only ~8Gb in
size and the transactional volume is not much either.
However, when the backups run, the iowait according to
'top' hovers between 50-70% which causes our
application to time-out via Web Logic 6.0.
The developers can't explain why the timeouts are
occurring (WLS 6.0 is a new upgrade from 5.1). The
SysAdmin isn't much help either.
I have an opportunity to rebuild the database on
another machine and use RAID 1+0 -- the thought being
that we are choking ourselves with Raid-5 when the hot
backups are performing the cp's (copies) and then the
files are compressed.
My first question is, how is the data distributed
across the drives in my Raid-5 configuration? Is each
disk being filled contiguously in series or is the
data being spread around in a pseudo-striping manner?
My second question/dilema is, the new array (another
A1000) will have 6 18Gb drives and with Raid 1+0 that
shrinks to 3 drives of usable space for everything
except redo and archive. 4 9Gb drives will be added in
two mirrored sets, one for redo and the other for
archive. I'm afraid that I will see worse I/O
performance with the new array because it has so fewer
physical drives, thus eliminating the benefit of not
having to write the parity info.
Do you concur? Knowing the two arrays I have to work
with, which would be the better configuration?
Any suggestions, recommendations would VERY much be
appreciated.
Thanks again for the feedback.
-w
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