Re: Is Raid 5 really that bad for Oracle?

niall.litchfield_at_dial.pipex.com (Niall Litchfield) wrote in message news:<b6beca79.0408020226.19e847f9_at_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).

I know a hardware-oriented IS manager who disputes that very thing. Given a W2K 2+GHz dual Xeon, the argument is that the dual controllers to the raid are going to be faster than the motherboard can hand things off to a mirrored C drive. I get the "trust me" response if I try to put anything anywhere but the raid-5. And there really isn't enough room to do otherwise when you start adding in backups and arcs and future data.

>
> 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

"The new Number Two." (BBCA is rerunning The Prisoner).

> 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

jg

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