[ILUG] Why RAID
John P. Looney
valen at tuatha.org
Tue Jul 13 13:47:22 IST 2004
On Tue, Jul 13, 2004 at 01:38:31PM +0100, Paul Jakma mentioned:
> Ouch. RAID1+0 on four disks, so you get capacity and speed of
> two-disk RAID0 but reliability of four disks where you can only
> tolerate one failure? You'd be better off with RAID5 on three disks +
> hot spare - sameish read performance, same capacity, but you can
> tolerate two failures (provided second failure doesnt occur before
> hot spare has synced).
No, if you raid 1 before you raid 0, you can lose half you disks, and
keep going (though they have to be the right half!). It's the
configuration Sun recommend in all installations to people that have loads
of money; RAID1+0 and a hot spare (or two). I'd only recommend it in cases
where there are a lot of writes - like mail and database servers. It'll
beat RAID5 by a good margin.
I'll be building a new mail server soon, with 6 15kRPM SCSI disks in it;
I'll have a go with bonnie, and see what we get for RAID1+0 and RAID5.
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