[iSCSI] Trying to reach max disk throughput

[Ben RUBSON]

> On 10 Aug 2016, at 15:27, Ben RUBSON <ben.rubson at gmail.com> wrote:
> 
>> 
>> On 10 Aug 2016, at 13:44, Edward Tomasz Napierała <trasz at FreeBSD.org> wrote:
>> 
>> On 0810T1154, Ben RUBSON wrote:
>>> Hello,
>>> 
>>> I'm facing something strange with iSCSI, I can't manage to reach the expected disk throughput using one (read or write) thread.
>> 
>> [..]
>> 
>>> ### Initiator : iscsi disk throughput :
>>> 
>>> ## dd if=/dev/da8 of=/dev/null bs=$((128*1024)) count=81920
>>> 10737418240 bytes transferred in 34.731815 secs (309152234 bytes/sec) - 295MB/s
>>> 
>>> With 2 parallel dd jobs : 345MB/s
>>> With 4 parallel dd jobs : 502MB/s
>>> 
>>> 
>>> 
>>> ### Questions :
>>> 
>>> Why such a difference ?
>>> Where are the 167MB/s (462-295) lost ?
>> 
>> Network delays, I suppose.
> 
> I just saw that iSER is available in FreeBSD 11, let's install BETA4 and give it a try.

OK, as a target I used Linux TGT, as iSER target (isert) is not FreeBSD available yet.

### Target : local disk throughput, one thread :
# dd if=/dev/da8 of=/dev/null bs=$((128*1024)) count=81920
10737418240 bytes (11 GB) copied, 21.3898 s, 502 MB/s

### Initiator : iscsi disk throughput, one thread :
# dd if=/dev/da8 of=/dev/null bs=$((128*1024)) count=81920
10737418240 bytes transferred in 34.938676 secs (307321843 bytes/sec) - 293 MB/s

### Initiator : iSER disk throughput, one thread :
# dd if=/dev/da8 of=/dev/null bs=$((128*1024)) count=81920
10737418240 bytes transferred in 20.371947 secs (527068838 bytes/sec) - 502 MB/s

No need to comment, let's wait for the FreeBSD iSER target then !

Ben