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Re: Is Raid 5 really that bad for Oracle?

From: Niall Litchfield <niall.litchfield_at_dial.pipex.com>
Date: 2 Aug 2004 03:26:14 -0700
Message-ID: <b6beca79.0408020226.19e847f9@posting.google.com>


"joe bayer" <joebayerii(no-spam)@hotmail.com> wrote in message news:<qDPOc.1753$%J6.1677_at_trndny07>...
> I am quoting from Jonathan Lewis's book, Practical Oracle 8i, page 206
>
> Raid 5 has an undeservedly bad reputation as far as Oracle database systems
> are concerned. ....
> However, for most small systems, it is almost necessary and perfectly
> acceptable; and for many large systems it is totally adequate.

I'm not sure that I buy that it is almost necessary - it would be common in 'small' systems.

I'd suggest that whether RAID5 is technically appropriate or not depends entirely on the application (that looks to be behind some of Jonathan's words too). No-one disputes (with the odd storage vendor sales droid exception) that RAID5 has a rather serious write penalty and so is slower than RAID10 (for the same capacity).

The question it seems to me is, does my system require more IO per second than my storage can give it - if so i'm going to be in trouble and want the fastest possible storage subsystem. if however it doesn't then probably I want the cheapest appropriate storage system.

unfortunately it would appear that reliably measuring and predicting IO is rather difficult and so is generally left undone, then storage is bought on the basis of

1, the deal that the vendor can offer you 2, prejudice from either the sysadmins or dbas or
3, the fastest, most expensive hardware I can possibly get just in case.

Of course if we buy these clever new virtualized storage technologies then measuring io requirements of your app might be possible, but predicting what IO you'll get out of your device becomes somewhat problematic.

Niall Received on Mon Aug 02 2004 - 05:26:14 CDT

Original text of this message

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