SnapShot Overview 1–3
Hitachi Simple Modular Storage Copy-on-Write SnapShot User’s Guide
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Figure 1-1: SnapShot functional components

The following sections describe how these components work together.
How SnapShot Works
SnapShot creates a virtual duplicate volume of another volume. This
volume “pair” is created when you:
• Select a volume that you want to replicate
• Identify another volume that will contain the copy
• Associate the primary and secondary volumes
• Create a snapshot of the primary volume data in the virtual (secondary)
volume.
Until the new or re-synchronized pair is split, all data written to the primary
volume is also copied to the virtual volume. When the pair is split, the
primary volume continues being updated, but the snapshot in the virtual
volume remains as it was at the time of the split. The pair can be made
identical again by re-synchronizing changes from primary-to-secondary or
secondary-to-primary.