On Mon, Oct 29, 2007 at 08:41:39AM +0100, Luca Berra wrote:
> consider a storage with 64 spt, an io size of 4k and partition starting
> at sector 63.
> first io request will require two ios from the storage (1 for sector 63,
> and one for sectors 64 to 70)
> the next 7 io (71-78,79-86,97-94,95-102,103-110,111-118,119-126) will be
> on the same track
> the 8th will again require to be split, and so on.
> this causes the storage to do 1 unnecessary io every 8. YMMV.
That's only true for random reads. If the OS does sufficient read-ahead
then sequential reads are affected much less. But the killers are the
misaligned random writes since then (considering RAID5/6 for simplicity)
the stripe has to be read from all component disks before it can be
written back.
Gabor
--
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MTA SZTAKI Computer and Automation Research Institute
Hungarian Academy of Sciences
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