HP 3PAR StoreServ 7450 4-node HP 3PAR StoreServ Storage Concepts Guide (OS 3.1 - Page 47

Copy-on-Write Function, Base Volume and Virtual Copy Relationships, Snapshot Tree

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Page 47 highlights

See Figure 8 (page 47) for a more complex example of the possible relationships between a parent base volume and its virtual copies. Figure 8 Base Volume and Virtual Copy Relationships Copy-on-Write Function When a virtual volume or snapshot's source volume is written to, the copy-on-write function preserves the data that is to be overwritten. The data is copied to the snapshot space associated with the original virtual volume before the write operation is completed, and a pointer in the administration space points to the copied data. See Figure 9 (page 47) for an example of a sequence of snapshots. Figure 9 Snapshot Tree In the figure above: • S0 is the first virtual copy made of BaseVV. • S2 is the most recent virtual copy. Virtual Copy Snapshots 47

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See
Figure 8 (page 47)
for a more complex example of the possible relationships between a parent
base volume and its virtual copies.
Figure 8 Base Volume and Virtual Copy Relationships
Copy-on-Write Function
When a virtual volume or snapshot’s source volume is written to, the copy-on-write function preserves
the data that is to be overwritten. The data is copied to the snapshot space associated with the
original virtual volume before the write operation is completed, and a pointer in the administration
space points to the copied data.
See
Figure 9 (page 47)
for an example of a sequence of snapshots.
Figure 9 Snapshot Tree
In the figure above:
•
S0
is the first virtual copy made of
BaseVV
.
•
S2
is the most recent virtual copy.
Virtual Copy Snapshots
47