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Re: RAID and Oracle Installation

From: MotoX <rat_at_tat.a-tat.com>
Date: Wed, 8 Jul 1998 10:16:26 +0100
Message-ID: <899889306.3639.0.nnrp-06.c2de712e@news.demon.co.uk>

Dean Mah wrote in message <6nu54r$d8a_at_ds2.acs.ucalgary.ca>...
>I'm a total newbie when it comes to RAID, so please bear with me.
>
>We are thinking of installing Oracle 7.3.4 on AIX 4.3.1 with RAID-5. We
>will be using 3 physical disks to make up the array. How does RAID
>affect the OFA when installing?

If you use filesystems rather than raw devices, then it doesn't. The RAID array appears as a single 'hdisk' device under AIX. You can follow OFA by creating multiple root directories on this hdisk, even though they would in fact be on the same drives - so you can have a series of Logical Volumes, each with their own filesystems and mount points, just like it says in OFA (i.e., /u01, /u02, /u03, etc). BTW, I tend to use the db SID and data file type (ctrl, data, index, syst, temp, etc) in the LV name, it makes them much easier to track - especially if you later decide to go for raw devices.

>For instance, Oracle sets up 3
>different mount points for software during installation, is this needed
>anymore? How do you lay out redo logs, control files, and separation of
>data from indices? With only 3 disks what type of read/write
>performance can we expect?

Exactly the same as normal in terms of layout - see above. Of course the problem is that although the LVs and filesystems are separate, the underlying disks are all the same. You'll have to test performance and see what you get. If it ain't good enough, get some more disks and consider setting up multiple RAID groups and some mirrored, non-RAID groups (use LVM to mirror non-RAID groups). You can do this with SSA RAID adapters, although read the SSA Users Guide carefully for restrictions - there are some (oh, and you can't have striped *and* mirrored drives though LVM).

You might want to pull temp and redo out of the RAID set-up first. Likewise you might want to put them on raw. Do some testing and monitor both the Oracle datafile I/O (via V$ tables) and AIX I/O with 'monitor' and/or 'iostat'.

>Are there any gotchas that we should be wary
>of before jumping into this setup? Are there any Oracle with RAID
>installation papers/manuals out there?

Read the manuals for both LVM and SSA adapters carefully. Most Oracle books will give you some *simple* overviews of RAID, but they never commit themselves - they can't, because there are to many variables out there in the real world. Do your own testing and make your own decisions.

BTW, I strongly suggest you get more drives - 3 is not enough. And make sure you dedicate a hot-spare to your RAID set-up - I've already had one drive blow this year on a RAID 5 array, and the hot-spare was worth it's weight in gold.

MotoX.

>
>Thanks for any help you can provide,
>Dean
>
>
Received on Wed Jul 08 1998 - 04:16:26 CDT

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