Snapshot - D-Link DSN-6120 User Manual

Tips
The size of VD extension must be larger than original.
Caution
VD Extension cannot be executed during rebuilding or migration.

5.4 Snapshot

Snapshot-on-the-box captures the instant state of data in the target volume in a logical
sense. The underlying logic is Copy-on-Write -- moving out the data which would be
written to certain location where a write action occurs since the time of data capture. The
certain location, named as "Snap VD", is essentially a new VD which can be attached to a
LUN provisioned to a host as a disk like other ordinary VDs in the system. Rollback
restores the data back to the state of any time which was previously captured in case for
any unfortunate reason it might be (e.g. virus attack, data corruption, human errors and
so on). Snap VD is allocated within the same RG in which the snapshot is taken, we
suggest to reserve 20% of RG size or more for snapshot space. Please refer to the
following figure for snapshot concept.
Figure 5.3.2
Figure 5.4.1
84