[Stgt-devel] iSER tgtd performance

[Jernej Porenta]

Heya all,

I am using OSC git tgt tree for testing iSER with virtualization. My
research focus in on I/O performance in virtualization tehniques
(OpenVZ, VMWare server, Xen).

I am using CentOS5 + OFED1.2.5 where it is possible (on target and
OpenVZ) with Dell 1950 servers with 4GB ram with Mellanox single port
memfree infiniband cards.

On target node i usually setup my iSCSI target like this:
dd if=/dev/zero bs=1k count=1 seek=1048575 of=/dev/shm/tid1lun1
./tgtadm --lld iscsi --mode target --op new --tid 1 --targetname node1.nejc.net
./tgtadm --lld iscsi --mode target --op bind --tid 1 --initiator-address ALL
./tgtadm --lld iscsi --mode logicalunit --op new --tid 1 --lun 1
--backing-store /dev/shm/tid1lun1

And the performance from client using ib_iser, measured with disktest,
is around 1030MB/s which is quite impressive.

But the performance drops significantly when I increase the backing
store size to 3.5GB. Usually I get around 400MB/s. This
happens with tmpfs or with /dev/ram0.

Could you tell me what is the reason for that? Maybe internal kernel
stuff or anything else.

My init scripts on target and client are available here:
http://www.nejc.net/diploma/tgtd/

Thanks for developing such great software again...

cheers, Jernej