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capability of the tape library (number of drives, loaders, slots and available tapes; capacity of
tapes)
requirements for performing data recovery (maximal duration)
You need to analyze every argument that is relevant for your case and select the main criteria for the
choice. Then choose a backup scheme and specify the tape options.
Note, that any backup scheme in combination with different tape options will have quite different
results for efficient use of both tapes and devices.
Case to analyze
Suppose you need to automate a tape rotation for the case if:
the full size of the data to protect is approximately 320 GB
the approximate size of daily changes of data is about 16 GB
the approximate size of weekly changes of data is no more than 40 GB
tape capacity is 400 GB.
Let’s analyze the results of a combination of GFS and ToH schemes with different tape options for the
case.
All the below analyzed examples are a simplistic approach to a real case, but provide you with a
general conception of backup distribution onto tapes.
Legend for the case example figures
Any daily/incremental backup (16 GB) is shown in the figures as a green rectangle:
.
Weekly/differential backups (40 GB) are displayed as a blue rectangle:
.
Any full monthly backup (320 GB) is drawn in orange:
.
A whole tape (400 GB) is drawn as a gray rectangle:
.
Using the Grandfather-Father-Son tape rotation scheme
Tape rotation for the GFS backup scheme is substantially defined by the tape options specified for
the backup policy/plan to be created.
Assume the GFS settings are the following:
Start backup at:
11:00:00 PM
Back up on: Workdays
Weekly/Monthly: Friday
Keep backups:
Daily: 2 weeks; Weekly: 2 months; Monthly: 1 year
.
The main goal is to achieve full automation of tape rotation for these settings.
Keep in mind that a monthly backup is full, a weekly backup is differential, and a daily backup is
incremental in this implementation of the GFS scheme. The first backup is always full. So if the
