Re: Performance of SCST versus STGT

[Vladislav Bolkhovitin <vst@vlnb.net>]

Bart Van Assche wrote:
> On Jan 24, 2008 8:06 AM, Robin Humble <robin.humble+stgt@anu.edu.au> wrote:
> 
>>On Tue, Jan 22, 2008 at 01:32:08PM +0100, Bart Van Assche wrote:
>>
>>>.............................................................................................
>>>.                           .   STGT read     SCST read    .    STGT read      SCST read    .
>>>.                           .  performance   performance   .   performance    performance   .
>>>.                           .  (0.5K, MB/s)  (0.5K, MB/s)  .   (1 MB >MB/s)   (1 MB, MB/s)  .
>>>.............................................................................................
>>>. Ethernet (1 Gb/s network) .      77             78       .         77            89       .
>>>. IPoIB    (8 Gb/s network) .     163            185       .        201           239       .
>>>. iSER     (8 Gb/s network) .     250            N/A       .        360           N/A       .
>>>. SRP      (8 Gb/s network) .     N/A            421       .        N/A           683       .
>>>............................................................................................
>>
>>how are write speeds with SCST SRP?
>>for some kernels and tests tgt writes at >2x the read speed.

Robin,

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.

Vlad