Dell POWERVAULT MD3600I - Manual (Page 29)

• Standard virtual disks
• Thin provisioned virtual disks
• Consistency groups
To create a snapshot image, you must first create a snapshot group and reserve snapshot repository space for the
virtual disk. The repository space is based on a percentage of the current virtual disk reserve.
You can delete the oldest snapshot image in a snapshot group either manually or you can automate the process by
enabling the Auto-Delete setting for the snapshot group. When a snapshot image is deleted, its definition is removed
from the system, and the space occupied by the snapshot image in the repository is released and made available for
reuse within the snapshot group.
Snapshot Virtual Disks (Legacy)
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. 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. 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 a write occurs to the
virtual disk. 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.
Snapshot (Legacy) 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.
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 can result in data
loss or an inaccessible snapshot.
Virtual Disk Copy
Virtual disk copy is a premium feature you can use to:
• Back up data.
• Copy data from disk groups that use smaller-capacity physical disks to disk groups using greater capacity
physical disks.
• Restore snapshot virtual disk data to the source virtual disk.
Virtual disk copy generates a full copy of data from the source virtual disk to the target virtual disk in a storage array.
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