HP 3PAR InForm OS 3.1.1 Concepts Guide

Figure 9 Snapshot Tree
The relationships between the virtual copies derived from a base volume can be represented as a
tree. In the example in Figure 9 (page 48), the base volume BaseVV is the starting point. In this
example, each new virtual copy of the original has its name incremented by 1.
Each copy of a copy has an additional level added to its name: in this example, the first copy of
S1 is S1_0, and a copy of S1_0 is S1_0_0. Unlike the automatic snapshots created for physical
copies, these snapshots are not assigned names by the system.
NOTE: The naming convention used in the example above is recommended, but it is not enforced
by the system. You can name each virtual volume and virtual copy at the time of creation.
The following rules are enforced by the system when you create a snapshot:
• The tree grows in alternating layers of read/write and read-only snapshots. You can only
make a read-only copy of a read/write volume, and you can only make a read/write copy
of a read-only volume.
• A maximum of 256 read/write virtual copies can be made from one read-only virtual volume.
• A maximum of 500 virtual copies can be made from one base volume.
• A virtual volume cannot be deleted if a child copy of it exists. For example, S1 cannot be
removed unless S1_0, S1_0_0, and S1_0_1 are deleted first.
Copy-of and Parent Relationships
In the example in Figure 9 (page 48), there are two different tree structures: the solid arrows show
the copy-of relationships, and the dashed arrows show the parent relationship. For example, S0
is a read-only copy of BaseVV, and S1 is the parent of S0. The copy-of relationship simply shows
48 Virtual Volumes