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Using Your RAID Enclosure 45
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, which makes a backup copy of data the instant an error
occurs. 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.