Some Systems and Variations
Friday Tape Backup Method
In this method, you use 6 tapes/devices.- Monday
- Tuesday
- Wednesday
- Thursday
- Friday1
- Friday2
Each evening you put the appropriate tape in. On Friday you alternate between the two Friday tapes.
On Monday you take offsite the Friday backup just used and bring back the Friday tape
which is offsite.
Advantages: Simple
Disadvantages: Can go back at most two weeks. Must be disciplined in taking tapes
offsite and bringing back so that Friday tape is always available on Friday.
Extensions: Can have any number of Friday tapes to enable older backups to be stored.
Weekly and Monthly Combination
Monday to Thursday are backed-up as above. The first Friday of the month, a monthly tape is
used (these are rotated depending on how many months back you wish to go). Friday tapes can be
rotated either bi-weekly, tri-weekly or use 4 to have a tape for every other Friday in the month.
Advantages: Gives a broad coverage of dates, should a backup be needed from several months ago.
Disadvantages: Can be confusing. Requires more tapes. Must be disciplined in taking
tapes offsite and bringing back so that Friday tape is always available on Friday.
Tower of Hannoi Method
This method can be used with any number of tapes and they are alternated each day.
It is best shown in an example :-
Using 3 tapes :-
TAPE1
TAPE2
TAPE1
TAPE3
TAPE1
TAPE2
TAPE1
...repeat
Using 4 tapes :-
TAPE1
TAPE2
TAPE1
TAPE3
TAPE1
TAPE2
TAPE1
TAPE4
TAPE1
TAPE2
TAPE1
TAPE3
TAPE1
TAPE2
TAPE1
...repeat
Then tapes 2, 3 (, 4, etc) are rotated offsite.
Advantages: Can cover a large date range with less tapes.
Disadvantages: Can be confusing, so a schedule needs to be printed.
Quad Backup, Tower of Hanoi Scheduler
