Incremental Backups

Incremental Backups

Incremental backups can use fewer tapes to provide the same level of protection as repeatedly backing up the entire filesystem. They are also faster than backing up every file on the system.

An incremental scheme for a particular filesystem looks something like this:

On the first day, back up the entire filesystem. This is a monthly backup.
On the second through seventh days, back up only the files that changed from the previous day. These are daily backups.
On the eighth day, back up all the files that changed the previous week. This is a weekly backup.
Repeat steps 2 and 3 for four weeks (about one month).
After four weeks (about a month), start over, repeating steps 1 through 4.

You can recycle daily tapes every month, or whenever you feel safe about doing so. You can keep the weekly tapes for a few months. You should keep the monthly tapes for about one year before recycling them.