Hello
Pretty new to ESXI / iSCSI so please bear with me 
I've setup a test rig with a bare metal FreeNas providing iSCSI storage to an ESXi server.
The iSCSI networking is done via a direct cable (no switch / VLAN) with two Intel I350 Gigabit NIC
I created and fairly basic Windows VM and started to play around. Things seemed initially ok but as soon as I got into (relatively) heavy I/O (extracting a zip !) I get errors on the windows machine.
Looking into the ESX logs I see messages such as
Device
t10.FreeBSD_iSCSI_Disk______90b11c5173500-
00_________________ performance has
deteriorated. I/O latency increased from average
value of 5350 microseconds to 964280
microseconds.
warning
07/07/2013 13:52:03
win-cmsvugj19gc.nest.local
Nothing obvious reported on the FreeNas side, though.
Any idea / suggestion how to diagnose this ?