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Protecting virtual machines in clusters with CSV storage

Updated: November 1, 2013

Applies To: System Center 2012 - Data Protection Manager, System Center 2012 R2 Data Protection Manager, System Center 2012 SP1 - Data Protection Manager

Data Protection Manager (DPM) in System Center 2012 can back up virtual machines that are using Cluster Shared Volume (CSV) storage.

CSV overview

CSV is a feature of failover clustering that was introduced in Windows Server 2008 R2. CSV allows you to store multiple virtual machines running on multiple hosts in a cluster on a single storage volume. A CSV is a shared single disk that contains an NTFS volume. Multiple virtual machines can be stored on a CSV, and the CSV can be accessed by multiple Hyper-V host servers installed on failover cluster nodes. You can have multiple CSVs in a Hyper-V cluster. Typically, all of the virtual hard disks (VHDs) of virtual machines in the cluster are stored on a common CSV, so that any node in the cluster can access the VHDs.

Direct and Redirect I/O

Each Hyper-V host has a direct path (direct I/O) to the CSV storage Logical Unit Number (LUN). However, in Windows Server 2008 R2 there are a couple of limitations:

  • For some actions, including DPM backup, the CSV coordinator takes control of the volume and uses redirected instead of direct I/O. With redirection, storage operations are no longer through a host’s direct SAN connection, but are instead routed through the CSV coordinator. This has a direct impact on performance.

  • CSV backup is serialized, so that only one virtual machine on a CSV is backed up at a time.

In Windows Server 2012, these limitations were removed:

  • Redirection is no longer used.

  • CSV backup is now parallel and not serialized.

You can learn more about CSV changes in the TechEd presentation: Windows Server 2012 in Cluster Shared Volumes Reborn in Windows Server 2012: Deep Dive.

Using VSS

DPM works seamlessly with Volume Shadow Copy Services (VSS) to ensure that consistent versions of virtual machines are backed up without affecting virtual machine availability and access. Using VSS you can u to back up entire virtual machines at the host or storage level, so that their contents are backed up in a consistent state. VSS pauses the virtual machines, takes a snapshot, and enables backup of the file system and VSS-aware applications.

You can back up CSVs with a hardware VSS provider or with software VSS integrated in the Windows operating system.

  • Prior to Windows Server 2012, using software VSS entailed the use of redirected I/O from the time the backup starts to the time it finishes, and used serialization, thus impacting performance. This limitation is removed in Windows Server 2012.

  • Hardware VSS does not require serialization and redirected I/O is only used when the snapshot is created. If you are running Windows Server 2008 R2 then using hardware VSS is recommended. After the snapshot is created, DPM starts to replicate the data from the snapshot to the DPM server. After the replication is completed, the DPM protection agent deletes the hardware snapshot.

For additional resources, see Information and Support for System Center 2012.

Tip: Use this query to find online documentation in the TechNet Library for System Center 2012. For instructions and examples, see Search the System Center 2012 Documentation Library.
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