HP Application Recovery Manager software A.06.10 Concepts guide (March 2008)

Figure 6 Creating a vsnap
1. At time T
0
, only pointers are copied to the target, as for a standard snapshot,
but no space is reserved for the target volumes. The snapshot takes up no storage
space other than that required for the pointers.
2. After snapshot creation, if T
0
source data needs to be updated, “copy-on-write”
is used, as in standard snapshots. Storage space is required only for the changed
data.
3. As with standard snapshots, the snapshot is now partly real and partly virtual.
Characteristics of vsnaps
• Like standard snapshots, a vsnap is not an independent duplicate of the original
data.
• Vsnaps require independent disk capacity management to guarantee enough
space for replica growth. If space on the array runs out, snapshot updates will
fail, and it could affect general array operation.
• They are space-efficient. The vsnap only uses the space is needs.
• They are intended to be short-lived. Since the storage requirement for vsnaps is
dynamic, the disk array may run out of space if there are many changes to the
source volumes after the snapshots have been created. Other storage requests to
a disk array can also cause the disk array to run out of storage.
Impact on application performance
Replication techniques28