Dell PowerVault MD3220 - Manual (Page 52)

52 Planning: MD3200 Series Storage Array Terms and Concepts
online and user-accessible. When the backup is completed, the snapshot
virtual disk is no longer needed. 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, 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 can be created instantaneously, or can be scheduled, and
take up less overhead than a full physical copy process.
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.
CAUTION: 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.
CAUTION: 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 incorrectly identifying the snapshot virtual disk. This can
result in data loss or an inaccessible snapshot.
For more information on mapping the snapshot virtual disk to the secondary
node, see the Dell PowerVault MD3200 and MD3220 Storage Arrays With
Microsoft Windows Server Failover Clusters on dell.com/support/manuals.
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