SV: HELP: RAID-5 Killing Performance

In2Home User <user_at_forlano.in2home.co.uk>:

> We're running Oracle 8.0.5 on Solaris 2.6.
> Our database server is a Sun UltraSparc I 333MHz with 1GB of RAM.
> We have several disks, a RAID-5 array, and a local tape device.
>
> My DBA is utilizing the disks in the following manner:
>
> disk1 - os
> disk2 - home
> disk3 (mirrored) - archived redo logs
> disk4 (RAID-5) - control file, system, temp, oracle software
> disk5 (RAID-5) - control file, rbs, redo logs
> disk6 (RAID-5) - control file, tools, users, redo logs
>
> My largest concern is that having the redo logs on RAID-5 has
> got to be killing my performance. Ideally, they should be on a
> dedicated set of mirrored drives (then again, ideally I should have
> 22 separate disks, yeah). However, my DBA feels that its more
> important to have the archive logs on the dedicated mirrored disks.
>
> Anyone care to share their opinion as to how we might make better
> use of the above hardware setup? Would it make sense to write archive
> logs directly to tape and move the redo logs to the mirrored disks?

Yeah. I've worked a lot with databases on CLARiiON storage array systems while at Data General. The "quick fix" for your situation is to switch places between redo logs and the archive logs. Oracle (or any other serious database with transaction integrity for that matter) will consider a transaction completed until it has been safely written to the redo log. You really want the logs on the disks that will give you the best possible write performance. The setup above is likely to kill your performance, and I just don't understand the reasoning of your sysadm to place the archive logs on the mirrored pair, which would be a perfect location for the redo logs. One thing you might want to consider, if your hardware supports it, is to add another mirrored set and stripe them. That will increase your write performance too.

The situation isn't quite as bad if your RAID controller (you DO have hardware RAID, don't you?) has sufficient battery backed-up cache memory for the RAID 5 group. If your transaction volume is high we're probably talking a lot more than the 4 MB or so of cache that most smaller controllers comes with.

The archive logs are written asynchronously and won't be a performance bottleneck in most cases. Received on Tue Sep 14 1999 - 17:14:36 CDT