Re: Performance of SCST versus STGT

[Vladislav Bolkhovitin <vst-d+Crzxg7Rs0@public.gmane.org>]

Robin Humble wrote:
> On Thu, Jan 24, 2008 at 02:10:06PM +0300, Vladislav Bolkhovitin wrote:
> 
>>>On Jan 24, 2008 8:06 AM, Robin Humble <robin.humble+stgt-FCV4sgi5zeUQrrorzV6ljw@public.gmane.org> wrote:
>>>
>>>>how are write speeds with SCST SRP?
>>>>for some kernels and tests tgt writes at >2x the read speed.
>>
>>There is a fundamental difference between regular dd-like reads and writes: 
>>reads are sync, i.e. latency sensitive, but writes are async, i.e. latency 
>>insensitive. You should use O_DIRECT dd writes for the fair comparison.
> 
> I agree, although the vast majority of applications don't use O_DIRECT.

Sorry, it isn't about O_DIRECT usage. It's about latency bound or not 
workload.

> anwyay, the direct i/o results were in the email:
> 
>   direct i/o dd
>    write/read  800/751 MB/s
>      dd if=/dev/zero of=/dev/sdc bs=1M count=5000 oflag=direct
>      dd of=/dev/null if=/dev/sdc bs=1M count=5000 iflag=direct
> 
> I couldn't find a direct i/o option for lmdd.
> 
> cheers,
> robin
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