EMC FC4700 What Is EMC SnapView Software?

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EMC Fibre Channel Storage System Model FC4700 Configuration Planning Guide
About SnapView Snapshot Copy Software
What Is EMC SnapView Software?
EMC SnapView is a software application that captures a snapshot
image of a LUN and retains the image independently of subsequent
changes to the LUN. The snapshot image can serve as a base for
decision support, revision testing, backup, or in any situation where
you need a consistent, copyable image of real data.
SnapView can create or destroy a snapshot in seconds, regardless of
the LUN size, since it does not actually copy data. The snapshot
image consists of the unchanged LUN blocks and, for each block that
changes from the snapshot moment, a copy of the original block. The
software stores the copies of original blocks in a private LUN called
the snapshot cache. For any block, the copy happens only once, when
the block is first modified. In summary:
snapshot copy = unchanged-blocks-on-source-LUN + blocks-cached
As time passes, and I/O modifies the source LUN, the number of
blocks stored in the snapshot cache grows. However, the snapshot
copy, composed of all the unchanged blocks — some from the source
LUN and some from the snapshot cache — remains unchanged.
The snapshot copy does not reside on disk modules like a
conventional LUN. However, the snapshot copy appears as a
conventional LUN to another host. Any other server can access the
copy for data processing analysis, testing, or backup.
The following figure shows how a snapshot session works: the
production host with the source LUN, the snapshot cache, and
second host with access to the snapshot copy.