iSCSI/Multipathing - possible broadcom iSCSI offload issues?

[hotwired007]

I have a Dell R815 server with 8x Broadcom BCM5709 connected to a QSAN Q500-P10 SAN (16x 3TB) but i'm having an issue with the iSCSI/multipath performance - when doing perfomance tests with fio i am getting maximum throughput of 200MB/s on RAID0 when reading and massive CPU load.

When doing a write to the SAN i am getting over 900MB/s with the high CPU load.

Any suggestions on what i should be looking at?

 

[hotwired007]

had to swap to a different server - but TOE was enabled the high CPU was actually a high load speed - CPU usage was minimal.

It was the switch causing the issue - HP 2920-48G - i've created an iSCSI VLAN and turned on flow-control for all the iSCSI ports - read speeds are upto around 300mb with 4 NICs enabled and 450mb on writes.

as the SAN is only SATA and an atom CPU i can't expect much more!

I'll be swapping back later to see if i can get much higher speeds with more NIC i'm expecting 600mb/s read and 880 writes.