Snapshot Basics

The Point-in-Time Methodology:

Snapshot is implemented as the backup utility which preserves pint-in-time images of s source volume.

A sequence of snapshot actions through a time line is described and diagrammed as shown above. 

1. At T0, a snapshot image is taken.

2. At T1, the source volume receives updates from host.

3. At T2, the RAID firmware copies block-level differentials of the data that is to be overwritten by the T1 updates to the snapshot volume.

4. At T3, source volume receives another update.

5. Again, firmware copies differentials of the data that is overwritten by the T3 updates to the snapshot volume.

Snapshot Directory Structure:

Snapshot uses additional RAID volumes for storing shanpshot configuration profiles and block-level differentials in subordinate snapshot images.

Snapshot Container (SC):

A RAID volume (a logical drive, a logical volume, or one of the logical partitions) allocated for saving all configurations and directories refering to one or several source (production) volumes.

Snapshot Set (SS):

Directories that each contains snapshot related information for a specific source volume.

A Snapshot Container may include mulitple Snapshot Sets that refer to multiple source volume.

Snapshot Image (SI):

Each snapshot image keeps block-level differentials of the data overwritten by host writes since the time snapshot was taken for a specific source volume.

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