Grandfather, Father, Son
(GFS) A backup rotation scheme in which a "grandfather" backup is performed on the first Monday of each month, a "father" backup is performed on every other Monday and a "son" backup is performed on every other day of the week. Grandfather tapes are kept for a year, father tapes for a month and son tapes for a week. The exact schedule (and thus the number of tapes required) may vary, as may the choice of full backup or incremental backup, but the idea is that it should be possible to restore versions of any file of different ages: e.g. yesterday's, last week's or last year's version.