Celerra NX4 iSCSI performance

I am seeing huge fluctuations in read speed on my Windows 2008R2 host connecting to Celerra NX4 iSCSI target. I am seeing highs of ~145MB/s and lows of ~2MB/s. The average seems to be around 60-70MB/s but the performance graph is up and down like a yoyo. I am testing with HD_Speed (auto block size).

Before I raise a support ticket, can anyone tell me if this normal behaviour?

I would like to use an iSCSI LUN as a Cluster Shared Volume for use with Hyper-V. I have created a Hyper-V VM on the host which has its VHD on the iSCSI LUN and it feels horribly slow.

Host setup:

Host model: Dell PowerEdge R620

Host CPU: 2 x Xeon E5-2640

Host RAM: 64GB

Host OS: Windows 2008R2 SP1 (fully up to date)

MPIO enabled and configured with 2 connections

TCP Delayed ACK disabled

Dedicated Gbit Storage Network:

2 x Netgear GS724TS with Jumbo Frames enabled

1 switch in subnet 192.168.20.x with one connection to host and one connection to NX4

1 switch in subnet 192.168.30.x with one connection to host and one connection to NX4

Celerra NX4:

NAS software 6.0.65-2

Flare version 2.23.50.711,6.23.8 (1.2)

12 x 1TB SATA disks

1TB thin-provisioned LUN