Slow iSCSI but fast NAS share performance

Hi. The small company I work for is looking for a SAN to start using iSCSI volumes on some of our servers but we're getting very poor performance on the iSCSI connection to our DSS box. I've got a Dell PowerEdge R710 server (Server #1) on which I’ve installed the latest DSS v6. The specs of the servers are at the bottom of this post. I've setup a 200GB volume and configured a basic iSCSI target. From another identical PowerEdge R710 server (Server #2) running Windows Server 2008r2 x64 i was able to connect to the iSCSI target, and assign a drive letter. Both servers are connected to a Dell PowerConnect 2848 switch.

I then proceeded to some basic testing. I started with just some basic file I/O. I tried copying a 12GB file to and from Server #2 to Server #1. The transfer only averages about 60MB/sec. But the network usage is VERY strange. It either uses all of the 1Gb connection or none. A screenshot is below.

http://72.18.38.59/1s.jpg

I've tried setting up the iSCSI connection from a different server and the exact same thing happened.....60MB/sec and wild swings in network usage when copying to and from Server #1.

I then set up a 100GB NAS share in DSS and mapped that share to a network drive on Server #2. A screenshot of the network usage is below.

http://72.18.38.59/2s.jpg

116MB/sec!

As you can see the performance is much better and MUCH more consistent.

So my question is why? What is up with the iSCSI target on the DSS server that wrecks the performance so badly? Any suggestions are greatly appreciated!

Thanks,

zlock
Prospective DSS Customer




Specs for both Dell PowerEdge R710 Servers:
2x Intel Xeon x5570 processors
64GB RAM
PERC H700 RAID controller
2x 15,000rpm 146GB SAS drives in RAID-1
6x 15,000rpm 146GB SAS drives in RAID-5
1 Gb network connection thru integrated Broadcom NetXtreme NIC

Create a support ticket, and send us the logs.