Re: Slow file transfer speeds with CFQ IO scheduler in some cases

[Vladislav Bolkhovitin <vst@vlnb.net>]

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.

Sorry,
Vlad