Apple Mac OS X Server (Version 10.6 Snow Leopard) - Manual (Page 34)

Understanding Backup Scheduling
Backing up files requires time and resources. Before deciding on a backup plan,
consider the following questions:
How much data will be backed up? Â
How much time will the backup take? Â
When does the backup need to happen? Â
What else is the computer doing during that time? Â
What sort of resource allocation will be necessary? Â
For example, how much network bandwidth is necessary to accommodate the load?
How much space on backup drives, or how many backup tapes are required? What
sort of drain on computing resources will occur during backup? What personnel are
necessary for the backup?
You will find that different kinds of backup require different answers to these
questions. For example, an incremental file copy might take less time and copy less
data than a full file copy (because only a fraction of any given data set will have
changed since the last backup).
Therefore an incremental backup might be scheduled during a normal use period
because the impact to users and systems may be very low. However, a full image
backup might have a very strong impact for users and systems, if done during the
normal use period.
Choosing a Backup Rotation Scheme
A backup rotation scheme determines the most efficient way to back up data over a
specific period of time. An example of a rotation scheme is the grandfather-father-son
rotation scheme. In this scheme, you perform incremental daily backups (son), and full
weekly (father) and monthly (grandfather) backups.
In the grandfather-father-son rotation scheme, the number of media sets you use for
backup determines how much backup history you have. For example, if you use eight
backup sets for daily backups, you have eight days of daily backup history because
you’ll recycle media sets every eight days.
Understanding Restores
No backup policy or solution is complete without having accompanying plans for data
restoration. Depending on what is being restored, you may have different practices
and procedures. For example, your organization may have specific tolerances for how
long critical systems can be out of use while the data is restored.
34 Chapter 2 Planning Server Usage