3PAR InForm® OS 2.2.4 Concepts Guide (320-200085 Rev B, March 2009)

8.8
Virtual Volume Types and Variations
3PAR InForm OS Concepts Guide InForm OS Version 2.2.4
Read-only and read/write copies must alternate. You can only make a read-only copy of a read/
write volume and a read/write copy of a read-only volume. Because base volumes are always
read/write, you can only create read-only copies of a base volume (Figure 8-1):
Figure 8-1. Read-only Copies of Base Volumes
Furthermore, a read-only copy can have only one read/write virtual copy, but a read/write
virtual copy can have many read-only copies, as illustrated in Figure 8-2:
Figure 8-2. The Read-only and Read/Write Copy Relationship
BASE VOLUME (RW)
RO
RO
RO
RO
RO...
RW=read/write
RO=read-only
RW=read/write
RO=read-only
RO
RW
RO RO RO RO...
RW
RW
RW
RW