Dell PowerVault MD3220 - Manual (Page 158)

158 Configuration: Premium Feature—Snapshot Virtual Disks
The associated snapshot repository virtual disk must have sufficient capacity
to process the rollback operation and the write operations from the host. At
most, the snapshot repository virtual disk may need twice the size of the base
disk, plus additional metadata space equaling approximately 1/1000th (that
is, 0.1%) of the Base volume capacity.
NOTE: Due to host server write operations, the content in the snapshot virtual disk
may have changed since creation of the snapshot. The rollback operation includes
any changes made to the snapshot after it was created.
You can set priority for a rollback operation. Higher priority allocates more
system resources for the rollback operation and affects overall system
performance.
Rules and Guidelines for Performing a Snapshot Rollback
The following rules and guidelines apply to performing a snapshot rollback:
• Rolling back a base virtual disk to a snapshot virtual disk does not affect
the contents of the snapshot virtual disks.
• Only one snapshot rollback operation can be performed at a time.
• While a base virtual disk that is undergoing a rollback, you cannot create a
new snapshot virtual disks from that base virtual disk.
• A snapshot rollback cannot be started while any of these operations are
underway:
–
Virtual Disk Capacity Expansion
– Virtual Disk Expansion (VDE)
– RAID Level Migration
– Segment Size Migration
– Virtual Disk Copy
– Role Reversal (in remote replication)
• If the base virtual disk is a secondary virtual disk in a remote replication,
you cannot perform a snapshot rollback.
• If any capacity used in the associated snapshot repository virtual disk
contains unreadable sectors, the snapshot rollback fails.
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