Determining The Length Of The Full Data Recovery Period; Incremental Jobs And Full Data Recovery - HP BB118BV - StorageWorks Data Protector Express Package User Manual

Full reconstruction of data can be accomplished in two ways. The first method requires the most recent
full backup media and all of the incremental backup media since the last full backup tape. The second
method requires the most recent full backup media and the differential job from the previous day.
For example, to reconstruct the data for a Wednesday from a Simple-6 set rotation type, you will require
one of two media sets: either, the full backup media (or media set) from the previous end of week and all
of the incremental media sets from that week (that is, Monday's, Tuesday's and Wednesday's); or, the
full backup media set from the previous end of week and the differential media set from Wednesday. (In
some circumstances, the preceding full backup media set will be a monthly or yearly job and not a weekly
job.) As long as none of these media sets has been overwritten, full data recovery is possible.
The length of the data recovery period is determined by the number of daily incremental or differential
media sets, the number and frequency of full backup jobs (usually weekly jobs), and the media rotation
you selected for the job.
Incremental jobs are the shortest and smallest jobs to run, but they present some issues related to full data
recovery. The difference between an incremental and a differential backup is important -- incremental
backup jobs back up only files that have changed since the last full, differential or incremental backup,
while differential backup jobs back up all files changed since the last full backup. If incremental backup
media sets are overwritten or recycled before another full backup is performed, this can create a gap in
available data if you need to recover files from the overwritten media.
Exclusive use of incremental backup jobs to ensure full data recovery after a disaster is not recommended,
unless you are using a schedule that retains one full backup and all subsequent incremental backups
before overwriting any media. However, to ensure successful data recovery with incremental jobs, follow
these guidelines:
Have at least as many incremental media as there are days between full or differential backup jobs.
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For example, if you run full backup jobs every five days, have at least four incremental media; if you
run full backup jobs every seven days, have at least six incremental media.
Never recycle incremental media between differential or full backup jobs. If you run more than one
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incremental job in a row, be certain to not recycle any of the media used during this string of
incremental jobs.
Related topics
For more information about planning backups, see Tips, Techniques and Strategies on page 160. For a
description of the default backup schedules, see Scheduling Jobs on page 90.