A Description Of Tape Rotation Methods
There are a few types of tape rotation. After selecting your backup method, for example full or differential, it's important to figure out a tape rotation schedule. The tape rotation is basically how the tape is fed through the system. The most popular tape rotation type is the Grandfather, Father, Son method.
For the Grandfather, Father, Son tape rotation the tapes are labeled by the days of the week. Each Friday in the month is given a new tape. Each month in the year gets a new tape as well. If you have data backed up over weekends as well then tapes for those days are used too. So the tape rotation would be Monday to Friday on tape one with the following week being tape two and so on. Because not every month is four weeks long, a total of more than twenty tapes are needed in a year for this rotation method.
The Tower of Hanoi is another tape rotation type based on a game of the same name. The object of the game is to move rings of different sizes among three poles. The game starts with all of the rings on one pole and ends when they have all been moved to the next pole. One of the rules is that a ring can never go on top of one that is smaller so they must be moved in strategic order to accomplish the end result. When it comes to tape rotation the same theory applies. The same order is used in rotating the tapes. There are many theories why this is a good method but an obvious benefit is that older versions of the files remain in existence. There are variations to this rotation type regarding how many backups to do in a day. Altering the format too much could result in the loss of days or weeks worth of data.
Incremental tape rotation is also a method that may be appropriate, depending on data requirements. You need to be able to determine how long the copy of the data must be kept. Each tape is given a number and is then sectioned into increment sets per week. For example, the first week of tapes would be tape one through seven while the second week would run from tape two to tape eight. Week three uses tapes 3 to nine and so on for each week until the end of the cycle is reached. If the cycle were to end with tapes five to eleven then the following week would see tape one used again running from six and returning to one. This system is not limited to a month long cycle but can be used for up to a year if need be.
Tape rotation is a valuable backup system because it keeps an organized structure to ensure data is properly kept and not left to clutter. It's also a good way to save on using tapes. By rotating tapes they last longer and experience less wear and tear. There are no real disadvantages when it comes to tape rotation. Organization saves time and money in the long run. Select your preferred method of rotation and eliminate your data worries.