[Gllug] AMD 64 X 2 / CentOS 4.3 x86-64 SMP RAID 5 slow

[Nix]

On Wed, 13 Sep 2006, Garry Heaton prattled cheerily:
> I presumed because the MegaRAID bios showed the array to be built that
> everything was OK. CentOS also showed the logical disk with about 2/3 of the
> total of all 3 disks, ie. what you would expect for RAID 5 so what's gone wrong?

I was wondering if perhaps it does like md does: if the first thing it
runs is a reintegration (i.e. to get the parity correct), and if it's
not as good as md is at deprioritizing the reintegration if real I/O
comes through, then you might see really slow I/O to start with.

(On non-degraded RAID-5 or RAID-6, you can normally expect things to be
*faster* than without RAID on the average, because you're getting your
data in parallel off two disks rather than one: it doubles the transfer
rate.)

-- 
`In typical emacs fashion, it is both absurdly ornate and
 still not really what one wanted.' --- jdev
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