There is a common myth among DBAs that RAID 0 is necessary to improve
performance. Striping only helps for large sequential reads and writes and
can actually hinder smaller reads and writes, which are more common on OLTP.
Moreover, unless your hardware has enhanced performance characteristics for
striping, RAID 0 for two disks on the same controller can further reduce
performance. You must verify the performance characteristics of RAID 0 on
your particular array, and if necessary, ensure two striped disks are on
separate controllers.
Before using RAID 0 for your temp and archive logs, validate your use of
temp space and your volume of transactions. Unless you are performing very
large sorts or other types of queries allocating large amounts of temp
space, RAID 0 could reduce the performance of your applications. For
archive logs, is your volume of archive data large enough to benefit?
For RAID 1, you must be aware of where the disks are in relation to your
controllers. If you mirror two disks on the same controller, you will
almost always thrash performance. However, two disks sharing a pair of load
balanced controllers can be okay. You must know in advance what your
hardware can handle.
The most important things in configuring arrays are ensuring your I/O is
spread across multiple controllers evenly (load balanced) and that you have
sufficient cache. Do not skimp on your cache. For most applications a very
large RAID cache can lead to significant performance increases. High end
arrays typically have large caches and some will automatically load balance.
However, the less intelligent your disk subsystem, the more work you have to
do.
You have to estimate, verify, and test your configuration. Estimate your
I/O needs, verify that your hardware can handle your I/O needs, and test
your configuration with real data loads before deploying.
Good Luck!
Chris
----------------------------------------------------
Chris Weiss, Blueoak Database Engineering, LLC
http://www.blueoakdb.com
PH: 517-381-9305
CELL: 517-974-5634
eFAX: 801-340-0740
-----Original Message-----
From: O Donnell Kevin (Contractor)
[mailto:oracledba-ezmlmshield-x98353302.[Email address protected]
Sent: Tuesday, September 28, 2004 2:53 PM
To: LazyDBA Discussion
Subject: Questions about raid setup
Hello everyone,
I wanted to get some thoughts and opinions about different hardware raid
configurations for 9i databases. My plans are to implement 6 spans of raid 1
and two spans of raid 0. The raid 1 spans will be used for oracle home,
control files, redo and datafiles. The raid 0 will be used for temp and
archive logs. Any other suggestions, what does everyone else run?
This will be for multiple oltp instances.
Thanks
Kevin O'Donnell
Oracle Database Administrator
Information Delivery Systems
--------
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