[Stgt-devel] Performance of SCST versus STGT

Robin Humble robin.humble+stgt
Thu Jan 24 12:40:27 CET 2008

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 at anu.edu.au> 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.
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.


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