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2–4 Planning and Design
Hitachi Simple Modular Storage Copy-on-Write SnapShot User’s Guide
• If the snapshot is to be used as a disk-based backup available for online
recovery, you can determine the lifespan by multiplying the number of
generations of backup you want to keep online by the snapshot
frequency. For example:
Generations held = 4
Snapshot frequency = 4 hours
4 x 4 = 16 hours
V-VOL lifespan = 16 hours
Lifespan Based on Business Uses
• If you use snapshot data (the V-VOL) for testing an application, the
testing requirements determine the amount of time a snapshot is held.
• If snapshot data is used for development purposes, development
requirements may determine the time the snapshot is held.
• If snapshot data is used for business reports, the reporting
requirements can determine the backup’s lifespan.
Establishing the Number of V-VOLs that Are Required
V-VOL frequency and lifespan determine the number of V-VOLs your system
needs per P-VOL.
For example: Suppose your data must be backed up every 12 hours, and
business-use of the data in the V-VOL requires holding it for 48 hours. In
this case, your SnapShot system would require 4 V-VOLs, since there are
four 12-hour intervals during the 48-hour period. This is illustrated in
Figure 2-1.
•
Figure 2-1: V-VOL Frequency, Lifespan