A backup rotation scheme is a pre-calculated method of scheduling and managing the media for backing up data when for security reasons or cost-effectiveness multiple types of media are required.
The rotation scheme is designed to specify when and how each piece of removable storage is selected for a archiving and restoration.
It also includes how long the media is retained after it is used for backing up data.
There are four primary backup rotation schemes that have been defined by professionals who are responsible for data retention and cost of data storage media.
1.
Incremental backup: This backup method saves only the new or modified files onto the oldest media being used.
For example, a daily backup onto a set of 21 media (CDs, tape, flash, etc.
) would have a backup depth of 21 days.
Each day, the oldest media would be inserted when performing the backup.
This is a simple rotation scheme that can be managed by dating each media and performing the daily backups - some people after the third rotation discard the oldest after 21 days and add a new, unused media to the group.
The benefits of this method are its cost and the efficient use of media for short-term restoration.
2.
Grandfather-father-son backup: There are several methods of managing this rotation: by media, by generation, or by date.
The by-media method uses a different media for each generation of backup.
For example, grandfather or the third backup is always to tapes, the father or the second backup is always DVDs, and the son is always to rotating external drives.
The by-media method uses DVDs for three backups, then tapes for three backups, then external drives for three backups.
The by-date method has a sliding use of media every 4th day.
For example, the media sequence for daily backups is: Day 1: DVD, Day 2: tape, 3: external drive, 4: tape, 5: external drive, 6: DVD, 7: external drive, 8: DVD, 9: tape, etc.
Also the method may be defined as three separate sets of backups, such as daily, weekly and monthly.
The son or daily backup media is rotated on a daily basis with one advancing to father status each week.
The father or weekly backup is rotated on a weekly basis with one advancing to grandfather status each month.
Some IT professionals prefer to take one or more of the advanced backups to an offsite location for safekeeping.
3.
Three-Tape Hanoi Schedule: There is a 3-day, a 4-day, and a 5-day Hanoi schedule as well.
This method is for daily, weekly or monthly backups.
The idea is, for example, Media A is used every other day, media B after the second day is used every 4th day, and media C after the fourth day is used every 4th day.
Here is a schedule for reference: Day 1: Media A; Day 2: Media B; Day 3: Media A; Day 4: Media C; Day 5: Media A; Day 6: Media B; Day 7: Media A; Day 8: Media C.
4.
Incremented media method: This method has many arrangements and is somewhat like the grandfather-father-son method.
A set of numbered media is used until the end of the pre-calculated cycle.
Then the cycle is repeated using media numbered the same as the previous cycle, except incremented by one.
Next, the lowest numbered tape or DVD from the previous cycle is retired and kept permanently.
This supports you having access to every backup for one cycle and for one backup per cycle from previous backups.
This method has the advantage of ensuring even media wear, but definitely requires a schedule to be predetermined.
The system is generally too complex to remember the next media to be used so make up a schedule and assign media incrementally.
The rotation scheme is designed to specify when and how each piece of removable storage is selected for a archiving and restoration.
It also includes how long the media is retained after it is used for backing up data.
There are four primary backup rotation schemes that have been defined by professionals who are responsible for data retention and cost of data storage media.
1.
Incremental backup: This backup method saves only the new or modified files onto the oldest media being used.
For example, a daily backup onto a set of 21 media (CDs, tape, flash, etc.
) would have a backup depth of 21 days.
Each day, the oldest media would be inserted when performing the backup.
This is a simple rotation scheme that can be managed by dating each media and performing the daily backups - some people after the third rotation discard the oldest after 21 days and add a new, unused media to the group.
The benefits of this method are its cost and the efficient use of media for short-term restoration.
2.
Grandfather-father-son backup: There are several methods of managing this rotation: by media, by generation, or by date.
The by-media method uses a different media for each generation of backup.
For example, grandfather or the third backup is always to tapes, the father or the second backup is always DVDs, and the son is always to rotating external drives.
The by-media method uses DVDs for three backups, then tapes for three backups, then external drives for three backups.
The by-date method has a sliding use of media every 4th day.
For example, the media sequence for daily backups is: Day 1: DVD, Day 2: tape, 3: external drive, 4: tape, 5: external drive, 6: DVD, 7: external drive, 8: DVD, 9: tape, etc.
Also the method may be defined as three separate sets of backups, such as daily, weekly and monthly.
The son or daily backup media is rotated on a daily basis with one advancing to father status each week.
The father or weekly backup is rotated on a weekly basis with one advancing to grandfather status each month.
Some IT professionals prefer to take one or more of the advanced backups to an offsite location for safekeeping.
3.
Three-Tape Hanoi Schedule: There is a 3-day, a 4-day, and a 5-day Hanoi schedule as well.
This method is for daily, weekly or monthly backups.
The idea is, for example, Media A is used every other day, media B after the second day is used every 4th day, and media C after the fourth day is used every 4th day.
Here is a schedule for reference: Day 1: Media A; Day 2: Media B; Day 3: Media A; Day 4: Media C; Day 5: Media A; Day 6: Media B; Day 7: Media A; Day 8: Media C.
4.
Incremented media method: This method has many arrangements and is somewhat like the grandfather-father-son method.
A set of numbered media is used until the end of the pre-calculated cycle.
Then the cycle is repeated using media numbered the same as the previous cycle, except incremented by one.
Next, the lowest numbered tape or DVD from the previous cycle is retired and kept permanently.
This supports you having access to every backup for one cycle and for one backup per cycle from previous backups.
This method has the advantage of ensuring even media wear, but definitely requires a schedule to be predetermined.
The system is generally too complex to remember the next media to be used so make up a schedule and assign media incrementally.
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