Dell PowerVault MD3000 - Manual (Page 46)

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Using Your RAID Enclosure
Snapshot Virtual Disks
A snapshot is a point-in-time image of a virtual disk. The snapshot provides an image of the virtual disk
at the time the snapshot was created. Typically, you create a snapshot so that an application (for example,
a backup application) can access the snapshot and read the data while the source virtual disk remains
online and user-accessible. When the backup is completed, the snapshot virtual disk is no longer needed.
Another potential use would be to experiment with a few different configurations until you determine
which one is the best. You can create up to four snapshots per virtual disk.
Snapshots are used to recover previous versions of files that have changed since the snapshot was taken.
Snapshots are implemented using a copy-on-write algorithm. Data on a virtual disk is copied to the
snapshot repository before it is modified.
Snapshots are instantaneous and take up less overhead than a full physical copy process.
For further details on using snapshot virtual disks, see the MD Storage Manager User’s’ Guide.
Snapshot Repository Virtual Disk
When you create a snapshot virtual disk, it automatically creates a snapshot repository virtual disk. A
snapshot repository is a virtual disk created in the storage array as a resource for a snapshot virtual disk. A
snapshot repository virtual disk contains snapshot virtual disk metadata and copy-on-write data for a
particular snapshot virtual disk. The repository supports one snapshot only.
You cannot select a snapshot repository virtual disk as a source virtual disk or as a target virtual disk in a
virtual disk copy. If you select a Snapshot source virtual disk as the target virtual disk of a virtual disk
copy, you must disable all snapshot virtual disks associated with the source virtual disk.
NOTICE:
Before using the Snapshot Virtual Disks Premium Feature in a Windows Clustered configuration, you
must map the snapshot virtual disk to the cluster node that owns the source virtual disk. This ensures that the
cluster nodes correctly recognize the snapshot virtual disk.
Mapping the snapshot virtual disk to the node that does not own the source virtual disk before the Snapshot
enabling process is completed can result in the operating system misidentifying the snapshot virtual disk. This, in
turn, can result in data loss or an inaccessible snapshot.
For details on mapping the snapshot virtual disk to the secondary node, refer to the Dell PowerEdge Cluster
SE600W Systems Installation and Troubleshooting Guide
on support.dell.com.
Virtual Disk Service
The Microsoft Virtual Disk Service (VDS) is supported on your RAID storage array. Microsoft VDS is a
set of application programming interfaces (APIs) that provides a single interface for managing disks and
other storage hardware, including creating volumes on those disks.
The Microsoft VDS installer service for storage provisioning is available on the MD3000 Resource CD in
the \windows\VDS_VSS directory. For more information on VDS, see www.microsoft.com.