On Thu, May 22, 2008 at 12:01 PM, Warren Young <warren@xxxxxxxxxxx> wrote:
> At any rate, RAID-10 shouldn't be *slower*.
I've actually seen equipments where RAID-10 was slower for reading
than RAID-5 with the same number of disks. RAID-10 depends on the
ability of the controller of balancing reads between the two disks
(because as both have the same information, it can choose from which
to read). Most implementations in cheap controllers (cheap as opposed
to hundreds of thousands of dollars SAN controllers) do not implement
this in the smartest possible way.
With RAID-5 there is not such a choice, the information must be read
from the disk that holds it, which means all implementations must do
the right thing, which will end up striping reads across all (but one)
disks.
In any case, I've used RAID-5 with databases and it works pretty well.
The biggest problem with RAID-5 (especially on big volumes) would be
the time to reconstruct if a disk fails. But if you're using good
quality SCSI drives that tend to last long, I would consider using
RAID-5.
As with any other performance-related issue, the answer, as usual,
comes from the benchmarks you do with your own application. Anything
else would be just theoretical and could not even apply to your
particular case.
HTH,
Filipe
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