Selecting A Reasonable Time Between Snapshots; Establishing How Long A Copy Is Held (Copy Lifespan); Lifespan Based On Backup Requirements - Hitachi AMS2100 User Manual

Selecting a reasonable time between Snapshots

Establishing how long a copy is held (copy lifespan)

Lifespan based on backup requirements

Hitachi AMS 2000 Family Copy-on-Write SnapShot User Guide
Ideally, a business desires no data loss. But in the real world,
disasters occur and data is lost. You or your organization's
decision makers must decide the number of business
transactions, the number of hours required to key in lost data,
and so on.
If losing 4 hours of business transaction is acceptable, but not
more, backups should be planned every 4 hours. If 24 hours of
business transaction can be lost, backups may be planned every
24 hours.
Determining how often copies should be made is one of the factors
used to determine data pool size. The more time that elapses
between snapshots, the more data accumulates in the data pool.
Copy frequency may need to be modified to reduce the data pool
size.
The length of time between snapshots, if too short or too long, can
cause problems.
• When short periods are indicated by your company's business
needs, consider also that snapshots taken too frequently could
make it impossible to recognize logical errors in the storage
system. This would result in snapshots of bad data. How long
does it take to notice and correct such logical errors? The time
span for snapshots should provide ample time to locate and
correct logical errors in the storage system.
• When longer periods between snapshots are indicated by
business needs, consider that the longer the period, the more
data accumulates in the data pool. Longer periods between
backups require more space in the data pool.
This effect is multiplied if more than one V-VOL is used. If you have
two snapshots of the P-VOL, then two V-VOLs are tracking changes
to the P-VOL at the same time.
Copy lifespan is the length of time a copy (V-VOL) is held, before a
new backup is made to the volume. Lifespan is determined by two
factors:
• Your organization's data retention policy for holding onto backup
copies.
• Secondary business uses of the backup data.
• If the snapshot is to be used for tape backups, the minimum
lifespan must be => the time required to copy the data to tape.
For example:
Planning and design
2-3