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SubjectRe: Slow file transfer speeds with CFQ IO scheduler in some cases
Vladislav Bolkhovitin, on 03/19/2009 08:44 PM wrote:
> 6. Unexpected result. In case, when all IO threads work in the same IO
> context with CFQ increasing RA size *decreases* throughput. I think this
> is, because RA requests performed as single big READ requests, while
> requests coming from remote clients are much smaller in size (up to
> 256K), so, when the read by RA data transferred to the remote client on
> 100MB/s speed, the backstorage media gets rotated a bit, so the next
> read request must wait the rotation latency (~0.1ms on 7200RPM).
Oops, it's RP*M*, hence the full rotation latency is in 60 times more,
i.e. 8.3 ms.


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