HP StoreOnce D2D2500 Implementation Manual page 16

vRanger Retention Policy, Space Saving Technology, and Deduplication
The Retention Policy should be set based on the number of recovery points from which the organization needs to be
able to recover. Each recovery point is a previous backup. The parameter to define the number of recovery points is
the Savepoint count. This is a setting of the backup job as shown in Figure 14.
More Savepoints enable more recovery points, but at the expense of requiring more disk space for a bigger
Repository. A key benefit of using the StoreOnce Backup System for the Repository is that it deduplicates and
compresses the backups to enable more backups (Savepoints) to be stored on disk for longer retention.
Figure 14: vRanger Retention Policy and Space Saving Technology
To reduce the size of each backup sent to the StoreOnce Backup System, vRanger has Space Saving Technology. This
is configured using one of three options:
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•
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The space saving technology is one of the parameters that determine the size of the Repository required for a given
backup specification. The other key parameter is the deduplication ratio achieved in the StoreOnce Backup System.
The deduplication ratio will be higher with vRanger's Space Saving Technology set to "None" than when Space
Saving Technology is set to "Incremental" because the backup data stream will have more duplicate data. The end-to-
end data compaction is the product of the vRanger Space Saving Technology and the StoreOnce Backup System
deduplication and compression. Figure 15 is an indication of the end-to-end data compaction over time when using
the "None" and "Incremental" Space Saving Technology settings. The actual end to end compaction will be different
for each installation and dependent upon a number of factors as discussed above. The same factors will determine if
full backups or of a mix a Full Plus incremental backups will give the greatest end-to-end compaction. The other
advantages of each the Full and Full Plus Incremental vRanger Space Saving Technologies are described in
Figure 16.
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None—runs a full backup at each Savepoint. This will give the slowest backups but fastest recoveries.
Incremental—runs incremental (just changes since last backup job) backups between full backups. This will give the
fastest backups but slightly slower restores.
Differential—runs differential (just changes since last full backup job) backups between full backups. This will give
faster backups than selecting "none" and generally slightly faster restores than selecting "Incremental".