Slow Disk Performance on Native SAN for Hyper-V

[JTDC]

I have two identical Dell Poweredge T410 with dual X5650 processors, 64GB ram, Intel X540 10Gb nics, Intel I340-T4 nics, and two onboard Broadcom nics. The disks are configured into two RAID arrays on the Dell H700 controller with 1G onboard cache. The first array is RAID 1 with mirrored 2 terabyte WD SATA drives. This is where the Windows Server 2012 system is installed. The second array is 4 3 terabyte WD nearline SAS disks configured as RAID 10.

For my Starwind configuration I have both ports of the X540s cabled nic to nic between the servers, with one port for synchronization and the other for iSCSI. Jumbo frames are enabled on these ports. When testing the nics outside of Starwind, I reach more than 5 Gb speed on each port pair. However, when using a single Windows Server VM in starwind, utilization on both port pairs stays well below 2 Gb. During full synchronization, speed stays below 1 Gb on the synchronization port pair.

In terms of disk speed, when I test on the two host servers, I get great speeds on the RAID 10 arrays. However, when I test on the VM speeds are very slow, starting out at 100 Mbps and dropping to 20 Mpbs. There is nothing else running on either of the hosts. Speeds on the iSCSI port pair stay under 2 Gb while testing.

I have tried recreating the VM, changing cache size in Starwind, disabling and reenabling jumbo frames, tweaking other TCP setting on the nics, recreating and reformatting the RAID arrays, recreating and reformatting the iSCSI Starwing disks. I return to the same slow VM disk speeds and underutilization of the 10Gb nics. I have run out of ideas. I appreciate any assistance that can be offered. Thanks.

[JTDC]

This is a sample showing a typical Atto benchmark on the VM.

VM Disk Speed.png (21.52 KiB) Viewed 7842 times

This is a sample showing the maximum sync speed that I reach on the 10G nic.

Sync Channel Transfer.png (40.44 KiB) Viewed 7862 times

[Anatoly (staff)]

It looks like the disk aligns issue. Can I ask you to try to use GPT formatting on all NTFS volumes that are SAN related and run benchmarks after?

[JTDC]

Hi. Thanks for the reply. I am using GPT volumes and the Atto test I showed above is on a GPT volume. Any other ideas about what the problem might be?

[Anatoly (staff)]

I need to know the following information from you in order to provide a solution:
1. Operating system on servers participating in iSCSI SAN and client server OS
2. RAID array model, RAID level and stripe size used, caching mode of the array used to store HA images, Windows volume allocation unit size
3. NIC models, driver versions (driver manufacturer/release date) and NIC advanced settings (Jumbo Frames, iSCSI offload etc.)
4. Network scheme.
Also, there is a document for pre-production SAN benchmarking:
http://www.starwindsoftware.com/starwin ... ice-manual
And a list of advanced settings which should be implemented in order to gain higher performance in iSCSI environments:
http://www.starwindsoftware.com/forums/ ... t2293.html
http://www.starwindsoftware.com/forums/ ... t2296.html

Please provide me with the requested information and I will be able to further assist you in the troubleshooting