[ewg] Re: [Scst-devel] SRP performance in SCST

[Doron Shoham]

Bart Van Assche wrote:
> On Mon, Mar 10, 2008 at 3:20 PM, Doron Shoham <dorons at voltaire.com> wrote:
>>  I used the following commands:
>>  for write commands:
>>  sgp_dd of=/dev/sg1 if=/dev/zero bs=512 bpt=<from 2-512> thr=8 time=1 count=20M
>>  for read commands
>>  sgp_dd if=/dev/sg1 of=/dev/null bs=512 bpt=<from 2-512> thr=8 time=1 count=20M
>>
>>  And the results are (all in MB/s):
>>  bpt:            2       4       8       16      32      64      128     256     512
>>  Write           22.5    41.4    80.6    160     275     443     570     740     810
>>  Read            42      80      170     313     550     940     1200    1312    1300
>>
>>  What can be the reason for such difference between the bandwidth of Read and Write commands?
> 
> Can you please try to use direct I/O instead of buffered I/O ?
> 
> Bart.

I have tried to use dio but when the bpt was 128 (or higher) I got the following error:

echo 1 > /proc/scsi/sg/allow_dio

sgp_dd if=/dev/sg1 of=/dev/null bs=512 bpt=128 thr=8 time=1 count=5M dio=1
time to transfer data was 2.236290 secs, 1200.36 MB/sec
5242880+0 records in
5242880+0 records out
>> Direct IO requested but incomplete 40960 times


Doron