Re: RAID 0+1 and OFA

Glen A Stromquist <stromqgl_at_alpac.ca> wrote:
>I am just moving a database from a AIX machine to a Compaq Proliant 8000
>NT(2000) server. There are 10 separate 18 gig drives. I told our NT
>administrator that I would like a minimum of 5 mirrored drives to spread the
>datafiles across.
>
>They just came back to me and have it configured the following way - 1 18gig
>C: drive, 1 34 gig D: drive and 1 34 gig E: drive, and two hot swappable
>spare drives

So you have a single mirror pair on C:, and two-spindle mirrored stripe sets, on D and E ?

>His logic is that because there is only 3 scsi controller channels, treating
>them as three logical drives is the best way, as the contention will be on
>the channels more than the spindles themselves. I tend to disagree, am I
>right here? I still say that it should be 5 separate drives. This is our
>biggest and heaviest use database, and I want it done right the first time.

It depends (tm).

On the SCSI contention issue, you're probably right, unless you have some bizarre mismatch between the performance of your SCSI controllers and your disks. A modern 40MB/s + SCSI controller should comfortably handle four disks for a database I/O access pattern (i.e. it might have trouble if all disks are just linearly streaming data, but not if they have to stop and seek reasonably often).

Before you decide how to allocate your storage, you should work out what your I/O requirements are, and where you want online redo logs and archive logs. It may be that you have a single table that's heavily used enough to justify a stripe-set, I don't know. You have to analyse your application to decide where to reduce disk contention, and where to increase throughput.

-- 
Andrew Mobbs - http://www.chiark.greenend.org.uk/~andrewm/