Snapshot Technology Improving Data Availability and Redundancy
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Snapshot is a "picture" of what the data looks like. This is usually referred to as a metadata copy in a reserved space, meaning the data itself is not copied to another location--only the pointers to where the data actually resides are copied. This is also called a PIT (point-in-time) copy of the source volume. Using a technology called copy-on-write (COW), if a snapshot is in place and then someone tries to over-write the data on the original volume, the snapshot software (either subsystem firmware or software running on the host) will first copy the original block of data to a new location (a pool of storage dedicated to copy operations) before it lets the write happen. It then maps pointers to the new location when an application references the original data or back to the original location when the snapshot is referenced.
