The following example illustrates how to determine the number of media you need for a GFS rotation scheme:
Your company’s business hours are from Monday to Friday. You have specified daily incremental backups from Monday through Thursday, with a full backup on Friday. You have decided to retain monthly full backup data for six months before you recycle your media, and have specified that at least six monthly tapes are to be maintained in the Save Set of your media pool. In addition, you have specified that a minimum of four weekly tapes are to be retained in the Save Set.
Note: For more information about media pools, Save Sets, and Scratch Sets, see "Managing Devices and Media."
In the GFS rotation scheme you have selected, the incremental backups are the Son, the weekly full backups are the Father, and the monthly full backups are the Grandfather.
Your rotation scheme requires four daily incremental backups, requiring one tape for each day. Because the data these tapes contain is maintained on the weekly full backup, these tapes are recycled each week. Therefore, your scheme requires four daily (Son) tapes.
The backup performed each Friday, the weekly full backup, requires one tape for each week of the month. These tapes are retained for one month before they are recycled, and you have specified that a minimum of four tapes are to be maintained in the media pool Save Set. Therefore, you require a minimum of five weekly (Father) tapes.
The last full backup performed each month is the monthly backup. You specified that these tapes are to be retained for six months, and that six tapes are to be maintained in the media pool Save Set. The minimum number of monthly tapes required before the media recycles is six. Therefore, you need seven monthly (Grandfather) tapes.
The total media you need for this rotation scheme is 16.
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