|
|
To determine backup frequency, consider how often data changes. For example, determine if files change several times a day, daily, weekly, or monthly.
Typically, sites perform daily backups to preserve daily work. Daily backups ensure that only one day's work is lost in case of a disk failure. More frequent backups are necessary when data changes many times during the day and these changes are important and difficult to reconstruct.
Daily backups are usually incremental backups that record the changes since the last incremental or full backup. Incremental backups conserve resources because they use less storage and take less time to perform than full backups.
Full backups usually occur less frequently than incremental backups but should occur often enough to avoid accumulating consecutive incremental backups. A large number of incremental backups between full backups increases the time it takes to restore a file. The time increases because of the effort that is required to merge the incremental backups when files and directories upon restore.
Consider the following when setting the frequency for full backups:
Extend the time between full backups for the files that seldom change. A longer frequency uses fewer system resources. It also does not significantly increase recovery time because the incremental backups between full backups are smaller.
Shorter the time between full backups for the files that change frequently. A shorter frequency decreases restore time. A shorter time between full backups can also use fewer resources. It reduces the cumulative effect of the longer incremental backups that are necessary to keep up with frequent changes in the files.
To achieve the most efficient use of resources, ensure that most of the files in a given policy change at about the same rate. For example, assume that half of the files in a policy selection list change frequently enough to require a full backup every week. However, the remaining files seldom change and require monthly full backups only. If all the files are in the same policy, full backups are performed weekly on all the files. This wastes system resources because half the files need full backups only once a month. A better approach is to divide the backups into two policies, each with the appropriate backup schedule, or to use synthetic backups.