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In this configuration, you would use no more than nine tapes. You will use one tape for each day of the week, Monday through Thursday (four tapes) and one tape for each Friday of the month (four or five tapes, depending on how many Fridays there are in a month). A maximum of nine tapes will give you daily backups for a week and weekly backups for a month. Label the tapes Monday through Thursday, and Friday Week 1 through Friday Week 5.

Yearly Rotation

You can build a yearly backup on top of the monthly system. You’ll need 12 tapes, one for each month, labeled with the names of the months. Rename the last weekly, full backup of each month to the corresponding month. You

go from nine tapes to 21 tapes and gain the capability of going back a year to restore data. Only one day out of each month is available after you go back further than your current month.

Grandfather-Father-Son Rotation

A standard rotation scheme for tapes is the Grandfather-Father-Son (GFS) method. With this method, daily backups are differential, incremental, or full. Full backups are done once a week. The daily backups are known as the Son. The last full backup of the week is known as the Father. Because the daily tapes are reused after a week, they age only five days. The weekly tapes stay around for a month and are reused during the next month. The last full backup of the month is known as the monthly backup, or the Grandfather. The Grandfather tapes become the oldest, and you retain them for a year before reusing them. Figure 9.7 is an example of a GFS tape scheme.

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