AFAIK: RAID-5 accesses are always in stripes. All disks are read (or
written) no matter how small the original read/write request. Whereas, RAID0
can read just one disk for smaller requests. RAID5 does a lot more work for
smaller requests.
<>< Lance.
>> Can anyone explain why a software raid5 array of N disks has
>> significantly lower read performance than a raid0 array of N-1 disks?
>> I'm only considering the case where there are no drive failures.
>
>My guess would be that since the parity is striped (unlike raid4),
>that you'd actually have to figure up which drives have the data and
>which one to skip, instead of being able to blindly loop around all
>drives in the array like raid0. This is a WAG at best, though :)
>
>Pure read performance shouldn't suffer with parity calcs unless
>the array is rebuilding... or is there some case where it'd recalc
>the parity and rewrite it back out regardless? Hmmm
>
>James Manning
>--
>Miscellaneous Engineer --- IBM Netfinity Performance Development
>
