backup plan question

The allowed downtime has a significant impact on the investments into network
infrastructure and equipment needed for backups. For each type of data, list the
maximum acceptable downtime for recovery, that is, how long specific data can
be unavailable before recovered from a backup. For example, user files may be
restored in two days, while some business data in a large database would need
to be recovered in two hours.

Recovery time consists mainly of the time needed to access the media and the
time required to actually restore data to disks. A full system recovery takes more
time, because some additional steps are required. For more information, see
“Disaster recovery” on page 134.

How long should specific types of data be kept?
For each type of data, list how long the data must be kept. For example, you may
only need to keep user files for three weeks, while information about company
employees may be kept for five years.

How should media with backed up data be stored and maintained?
For each type of data, list how long the media with data must be kept in a vault,
a safe, external location, if you use one. For example, user files may not be stored
in a vault at all, while order information may be kept for five years, with
verification of each medium after two years.

To how many media sets should the data be written during backup?
Consider writing critical data to several media sets during backup to improve the
fault tolerance of such backups, or to enable multi-site vaulting. Object mirroring
increases the time needed for backup.