Windows 2008 R2 Hyper-V has really slow VMs disk access

Question

Wondering if anyone can help? I have noticed in a couple of Windows Server 2008 R2 Hyper-V scenarios, that the VM guests are often very slow. Disk access is especially slow.
In one situation their was only a couple of guest VMs, and they were running of mirrored IDE HDDs.  Performance improved significantly when I used two mirrored SSD hdds instead.
My other main situation is where the VHDs are stored on HP Lefthand P4300, over 2-nodes with 8 SATA hdds in each, using iSCSI.
So I ran a few tests with robocopy copying 4-6GB of files (mostly large) or whole VHDs (40GB or more), using HP4300 SATA, a newer HP 4330 SAS, a THECUS NAS with SATA hdds,  and an SSD in a THECUS NAS, and local SAS mirrored hdds. All using iSCSI except
the local SAS hdds.
You can see from results that Guests run considerably slower than host. Any ideas?
Sample data (although not always same background conditions of load etc):
From within Guest direct iSCSI to same (from HP 4330): 34MB/s
From other Guest using VHD (from HP4300) to direct iSCSI (from HP4330): 14MB/s
From within Guest using VHD (from HP4330) to same: 9MB/s
From within Guest using VHD (from HP4300) to VHD (from HP4330): 11MB/s
From within Guest using VHD (from HP4330) to VHD (from HP4330): 19MB/s
From within Guest using VHD (from THECUS SSD) to same VHD (from THECUS SSD): 18MB/s
From within Guest using VHD (from HP4300) to VHD (from THECUS SSD): 13MB/s
From within Host from HP4300 iSCSI to HP4330 iSCSI: 12MB/s
From within Host using VHD (from THECUS SSD) to same VHD (from THECUS SSD): 40MB/s
From within Host from HP4330 iSCSI to same HP4330 iSCSI: 232MB/s & 132MB/s
From within Host from HP4330 iSCSI to HP4300 iSCSI: 40MB/s & 57MB/s
From within Host from HP4300 iSCSI to same HP4300 iSCSI: 26MB/s & 47MB/s
From within Host from HP4300 iSCSI to Guest VHD (from THECUS SATA): 15MB/s

Answer 1

Hi aucj,
I would suggest to use host level ISCSI connection then build VM on that ISCSI disk .
please add more Vcpu for that VM then try to copy again (shutdown the other VMs ,in that online VM from one folder to another folder ).
Hp4330 ISCSI connection is 1GB , right ?
If yes , it should be with max 100M/s with the single ISCSI connection .
Best Regards
Elton Ji
We
are trying to better understand customer views on social support experience, so your participation in this
interview project would be greatly appreciated if you have time.
Thanks for helping make community forums a great place.