Microsoft has issued a hotfix designed to resolve some problems related to the backup and restoring of virtual machines in Windows Server 2008 R2.
According to the Redmond company, the issues have been dealt with and resolves will be provided with Service Pack 1 (SP1).
However, the software giant has recently delivered Windows 7 SP1 Release Candidate and Windows Server 2008 R2 SP1 RC to testers, and there is still quite a wait until the upgrade is released to manufacturing.
In this regard, customers that need their Hyper-V problems to go away as fast as possible have an alternative to SP1, namely KB 975354
“A Hyper-V update rollup package is available for a computer that is running Windows Server 2008 R2.”
The hotfix is designed to resolve no less than four issues, but at the same time Microsoft underlines that only customers affected by the specific range of problems described in the KB article should deploy the accompanying fixes.
Those not impacted by the glitches described by the Redmond company should only install SP1 when it will be made available in the first quarter of 2011, sometime by March 31st of the coming year.
Microsoft detailed the problems that the hotfix is set up to resolve:
“Issue 1 - Some Internet SCSI (iSCSI) connections are created in a virtual machine that is running Windows Server 2003. You back up this virtual machine on the virtual machine host server.
In this scenario, the error code 0x800423f4 occurs when you back up the virtual machine. Additionally, the following event is logged into the Hyper-V Virtual Machine Management Service event log:
The number of reverted volumes does not match the number of volumes in the snapshot set for virtual machine "'virtual machine name' (Virtual machine ID <GUID>)".
Issue 2 - Cluster shared volumes are enabled on a failover cluster for Hyper-V. Some virtual machines are saved on the same volume. But they are running on different nodes.
These virtual machines are backed up in parallel. In this scenario, the virtual machine backup operation fails.
Issue 3 - A virtual machine is being backed up on a server that is running Hyper-V. At the same time, an application backup operation is being performed in the same virtual machine. In this scenario, some data is truncated from the application backup in the virtual machine. Therefore, this behavior causes data loss.
Issue 4 - A virtual machine that has some snapshots is backed up on a server that is running Hyper-V. Then, this virtual machine is restored to another location. In this scenario, the restore operation fails and the virtual machine may be corrupted.”
At the same time, the Redmond company also provided customers with the analysis of each problem.
“Cause of Issue 1 - When a virtual machine is being backed up, the VSS writer of the server that is running Hyper-V makes a call to the guest virtual machine to check whether any iSCSI connections exists. This call has a default time-out of 60 seconds.
If this call does not return within the time limitation, the VSS writer of the server that is running Hyper-V incorrectly assumes that there is no iSCSI connection. Therefore, the backup operation fails.
Cause of Issue 2 - When the virtual machines on different nodes are backed up in parallel, every node waits to become the cluster shared volume owner to create the snapshots. However, the Cluster service moves the volume owner from one node to another node immediately after a snapshot is created without waiting for post-snapshot tasks to be completed.
If another node requests the same shared volume for a backup operation before the post-snapshot tasks are completed, the Cluster service changes the volume to another node. Therefore, the VSS writer that is in the previous node cannot find the cluster shared volume locally when it performs post-snapshot tasks. This behavior causes the virtual machine backup operation to fail.
Cause of Issue 3 - The application backup operation in the virtual machine is incorrectly affected by the virtual machine backup operation on the server that is running Hyper-V.
Cause of Issue 4 -The snapshot files are not restored successfully when you restore the virtual machine.”