Release Notes

6 Dell PS Series: Space Borrowing for Snapshots and Replicas | TR1084 | version 2
1.1 Snapshots
In a PS Series group, Snapshots are space-efficient, point-in-time copies of a volume that can be used to protect data
and are often used to recover data lost by human error and data corruption. Multiple snapshots of a volume can be
retained for data protection and are accessible to other hosts.
When a Snapshot of a volume is created, it does not initially consume any space (as the snapshot shares all data with
the volume), but instead is a set of pointers to the data in the base volume. As data is modified on the base volume,
disk space is allocated from the snapshot reserve to store the modified data. Meanwhile, the snapshot still points to
the original data pages so that the volume looks exactly like it did at the point in time when the snapshot was taken.
1.1.1 Snapshot reserve
In order to create snapshots of a volume, the administrator must allocate snapshot reserve to hold the snapshot data.
Snapshot reserve space is consumed from the local group and pool where the volume resides and is a percentage of a
volume to be used to store its snapshots.
Note: Because snapshot reserve is a percentage of the volume reserve, the amount of snapshot reserve space
fluctuates in direct proportion to a thin-provisioned volume reserve when data is dynamically written and deleted (for
example, when invoking SCSI UNMAP from Microsoft
®
Windows
®
, VMware
®
ESXi™ or Red Hat
®
Linux — see section 3).