Microsoft Virtualization Discussions

Pass Through Disk and backup LUN on Hyper-V 2008 R2



I've a 2008 R2 Hyper-V host and I need to have a LUN directly connected to my virtual machine for SQL best performance. I read this below in the tr3702:

4.4.2 Pass-Through Disks
Pass-through disks are disks that are attached directly to the Hyper-V parent, but assigned directly to a VM, and formatted with the child OS file system. A pass-through disk is best suited for large data (typically beyond 300 to 500GB) sets and extreme I/O requirements. One of the limitations associated with the use of pass-through disks with VMs is that Hyper-V snapshot copies are not supported. For this reason, NetApp recommends limiting use of pass-through disks in your Hyper-V environment, except where considered necessary.
NetApp Best Practice Recommendation While fixed-size VHDs are strongly recommended for the majority of VM configurations, they have some limitations. As such, NetApp recommends use of pass-through disks for VMs with large data sets, typically beyond 300 to 500GB, with extreme I/O requirements,

- How can I create and resize my LUN since the virtual machine ? I can only to do this since the controler ? Or if possible with SnapDrive ?

- How can I backup virtual machine and LUN in same time ?





- How can I create and resize my LUN since the virtual machine ? I can only to do this since the controler ? Or if possible with SnapDrive ?

Best option is to use SnapDrive for it

- How can I backup virtual machine and LUN in same time ?

You need to use SnapManager for Hyper-V




I'd recomend using iscsi LUN's directly connected to the VM guests and use snapdrive/SMSQL.


Ok but I/O are not better with path Through Disk method with FC connection?

I read this below (source:

From Page 26 of SDW 6.2 IAG:

SnapDrive supports Hyper-V pass-through disks; however, there are some limitations related to this
• SnapDrive does not support direct attached storage to a Hyper-V parent host.
Only Data ONTAP iSCSI and FC LUNs are supported.
• SnapDrive does not support LUNs already mapped to a Hyper-V parent host.
A pass-through disk must be freshly provisioned from a storage system to be added dynamically.

• Windows 2008 R2 does not support pass-through disks using IDE.
Windows 2008 R2 supports only SCSI disks.
• Micorosoft cluster shared volume (CSV) disks are not supported.
• Hyper-V does not support the SnapDrive space reclaimer feature.
• Pass-through LUN creation fails when Data ONTAP DSM is installed on Hyper-V virtual machines.
Note: Removing MPIO will not remove MPIO iSCSI sessions that SnapDrive might have been
using. After removing MPIO, you must remove existing iSCSI sessions and, if needed, create
new iSCSI sessions.
• Due to a Microsoft limitation, if a pass-through disk is down, the virtual machine to which the disk
is assigned cannot be rebooted.
To reboot the virtual machine, you must bring the pass-through disk back up, or remove it from the
virtual machine using Microsoft Hyper-V Manager or another Microsoft remote server management
If DataFabric Manager role-based access control is enabled on a SnapDrive for Windows Hyper-V
parent host, you cannot dynamically add or remove pass-through disks with SnapDrive in a Hyper-V
virtual machine.

Are you sure to use SnapDrive & SMSQL in this case ?


I recomend iscsi to the VM over pass through because it actually works.  "IF" you get everything working with pass through disks, then great, but in my experience so far, it does not work out well especially with snapdrive.  


The virtual machine and pass through / iSCSI LUN in the VM cannot be backed up at the same time. SnapManager for Hyper-V can be used to backup the VM itself, but that backup will not include data on iSCSI / pass through LUNs in the VM. Another SnapManager (SMSQL / SME / etc.) installed in the VM (guest OS) can be used to backup the data on pass through or iSCSI LUNs.