Dell PowerVault MD3420 - Manual (Page 112)

Snapshot Virtual Disks
A snapshot virtual disk is a point-in-time image of a virtual disk. It is typically created so that an
application, such as a backup, can access the snapshot virtual disk and read the data while the source
virtual disk remains online and accessible to hosts.
CAUTION: Before using the source virtual disk of a snapshot virtual disk as your target, you must
disable all snapshot virtual disks associated with the source virtual disk. By disabling the snapshot
virtual disks, you avoid altering the snapshot data if the source virtual disk is changed.
Creating a snapshot virtual disk automatically creates a snapshot repository virtual disk. The snapshot
repository virtual disk stores information about the data that has changed since the snapshot virtual disk
was created. Snapshot repository virtual disks cannot be selected as a source virtual disk or target virtual
disk in a virtual disk copy.
The virtual disk for which the point-in-time image is created is the source virtual disk and must be a
standard virtual disk in the storage array.
You can select snapshot virtual disks as the source virtual disk for a virtual disk copy. Selecting a snapshot
virtual disk is a good use of this feature, because it enables complete backups without significant impact
to the storage array I/O. However, some I/O processing resources are lost to the copy operation.
The Snapshot Virtual Disk feature can be used with the Virtual Disk Copy feature to back up data on the
same storage array and to restore the data on the snapshot virtual disk back to its original source virtual
disk.
Virtual Disk Copy
The Virtual Disk Copy premium feature copies data from one virtual disk (the source virtual disk) to
another virtual disk (the target virtual disk) within a single storage array. You can use this premium feature
to perform these functions:
• Copy data from disk groups that use smaller-capacity physical disks to disk groups that use larger-
capacity physical disks
• Back up data
• Restore snapshot virtual disk data to the base virtual disk.
You can use a primary virtual disk in a remote replication as a source virtual disk or a target virtual disk in
a virtual disk copy. You cannot use a secondary virtual disk as a source virtual disk or a target virtual disk.
NOTE: If you start a role reversal during a copy-in-progress, the copy fails and cannot be restarted.
Storage Partitioning
Storage partitioning enables hosts to share access to virtual disks in a storage array. You create a storage
partition when you define the following storage array assignments:
• A host
• A host group
• Virtual disk-to-logical unit number (LUN) mapping
The virtual disk-to-LUN mapping enables you to define which host group or host has access to a
particular virtual disk in the storage array.
After you create a virtual disk copy, the target virtual disk automatically becomes read
‑only to hosts to
ensure that the data is preserved. Hosts that have been mapped to a target virtual disk do not have write
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