I'm not sure if this would be a better suited question for the plain old Server 2012 forums, so feel free to move this topic moderators.
Quick back story on our infrastructure. We have been building our own servers for the past couple of years to serve as a private cloud foundation using SCVMM 2012 so that our engineers can build out and deploy VMs as needed without having to ask IT to do this for them. This has been working great up until recently when I decided to use Server 2012 after the recent release of SCVMM SP1 instead of 2008 R2 on our latest build.
All 4 machines are identical other than operating system, 3 of which are using 2008 R2 Enterprise and the most recent 2012 Standard. 2 of these boxes are running 4x2TB locally in a RAID10, one of them is using the Microsoft iSCSI initiator to a Microsoft iSCSI Target we setup that has a 8TB LUN and the latest Server 2012 is also using the iSCSI initiator storage to house VHDs and VM config files.
The Server 2008 R2 box currently has 24 VMs running with the iSCSI disk reporting a highest active time of 30%. The VMs work seamlessly and I've had no complaints.
The Server 2012 box currently has 12 VMs running with the iSCSI disk jumping between a highest active time of 10% and 100% and of course when it spikes to 100% the VMs become incredibly slow and sometimes completely non-responsive. Of course I'm getting complaints
left and right.
The NIC configuration on the hosts are identical since the motherboards are the same the NICs are the same. I'm trying to figure out why the IO is so terrible in 2012 but works fine in 2008 R2.