Tower of Hanoi Rotation Schedule
Tower of Hanoi got its name from an ancient Chinese game using
recursive techniques. In the game, you move a stack of disks
from one of the pegs to another peg and a smaller disk can only
be placed on a larger disk.
Like the game, many multiple media sets are rotated through in
incremental/differential and full backups. It uses more media
sets than GFS for increased safety.In this schedule, one media
set "A" is used every other backup session (daily sessions in
this example).Start Day 1 with "1" and repeat every other backup
(every other day).
The next media set "B" starts on the first non-"A" backup day and
repeats every fourth backup session. Media set "C" starts on the
first non-"A" or non-"B" backup day and repeats every eighth session.
Media set "D" starts on the first non-"A," non-"B," or non-"C" backup
day and repeats every sixteenth session. Media set "E"alternates with
media set "D."
| Media set |
Week's number |
| |
1 |
2 |
3 |
4 |
5 |
6 |
7 |
8 |
9 |
10 |
11 |
12 |
13 |
14 |
15 |
16 |
17 |
18 |
| A |
x |
|
x |
|
x |
|
x |
|
x |
|
x |
|
x |
|
x |
|
x |
|
| B |
|
x |
|
|
|
x |
|
|
|
x |
|
|
|
x |
|
|
|
x |
| C |
|
|
|
x |
|
|
|
|
|
|
|
x |
|
|
|
|
|
|
| D |
|
|
|
|
|
|
|
x |
|
|
|
|
|
|
|
|
|
|
| E |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
x |
|
|
With each additional media set added to the rotation scheme,
the backup history doubles.The frequently used media sets have
the most recent copies of a file, while less frequently used media
retain older versions. This schedule can be used in either a daily
or weekly rotation scheme. The decision regarding the frequency of
rotation should be based on the volume of data traffic. To maintain
the required history of file versions, a minimum of five media sets
should be used in the weekly rotation schedule, or eight for a daily
rotation scheme. As with the Grandfather-Father-Son rotation scheme,
media should be periodically removed from the rotation for archive
purposes.
See also: Round Robin, Backup Rotation
|
