Hitachi Copy-on Write SnapShot, User Manual, Page: 16 / 90

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SnapShot Overview
Hitachi Simple Modular Storage Copy-on-Write SnapShot User’s Guide
Volume Pairs—P-VOLs and V-VOLs
A volume pair is a relationship established by SnapShot between two
volumes. A pair consists of a production volume, which contains the original
data and is called the primary volume (P-VOL), and from 1 to 32 virtual
volumes (V-VOLs), which contain copies of the P-VOL. The P-VOL and its V-
VOL(s) are located in the same Simple Modular Storage system.
A V-VOL is a mirror image of the P-VOL at the time of the snapshot. Unlike
the P-VOL, which contains the actual data, the V-VOL is made up of pointers
to the data.
To maintain the snapshot image of the P-VOL as new data is being written
to the P-VOL, SnapShot copies data being replaced to the data pool. V-VOL
pointers are updated to reference the original data's new location in the
pool. Figure 1-2 illustrates SnapShot volumes and data pool interaction.