This may seem like an elementary question but it does need to be considered before entering into any in depth discussion about how to get the best from an autoloader/tape library? This point may be better addressed by asking a different question to start with - what should we not be doing with an autoloader?

Autoloaders should not be filled with tapes and left to their own devices as it does not offer adequate protection against physical disaster. If all your tapes are in the autoloader and it is destroyed in a fire, you have lost all your backups. If the servers you were backing up are all in the same room and were also destroyed by fire, you may as well have not spent the money on the autoloader in the first place - at least not from the physical disaster point of view.

Rotating tapes out of the autoloader and storing them off site is the only way to ensure secure and safe backups.

One advantage of having an autoloader is that it enables you to back up to multiple tapes without manual intervention. If you have a single tape drive in your server and the tape filled up overnight, a new one could not be inserted until the administrator started work in the morning, by which time you would not want to be backing up the server because users would want to be using it and so performance would be compromised for both activities. The autoloader allows a new tape to be supplied as and when it is needed.

Another advantage is that multiple servers can back up to one tape or set of tapes. If you have five servers with one drive in each you will obviously need five tapes to complete a set of backups. With a large capacity tape and drive in an autoloader, a complete full backup may only take up one or two tapes. Whilst this saves on tape costs and makes better use of each tape (a tape that is 50% used each night and overwritten next time it is used, will wear out as quickly as one that is 100% used each night), it also makes the administrator's job easier by giving them fewer tapes to keep track of.

This discussion outlines RM's minimum recommended retention policy:

• A weekly full backup kept for four weeks (requiring four tapes or sets of tapes).
• A daily differential backup four nights per week, each kept for a week (requiring four tapes or sets of tapes).
• At least one spare/scratch tape (or sets of tapes) in case of tape failure, or for  ad-hoc backups.
• A cleaning tape.

Note: It is possible to run full backups every night and dispense with differentials, but many sites now have so much data that a full backup takes over ten hours so is only feasible at weekends.

As you can see this requires a minimum of nine tapes and a cleaning tape that stays in the autoloader (highly recommended). In order to accommodate a retention period longer than four weeks, additional tapes will be required.

When terms such as 'Monday tape' etc. are used below, they refer to the tape that is used on a Monday; it does not mean that the label of the tape when viewed in Backup Exec is Monday. It is more likely to be a unique reference, something like 'Tape005' and when it wears out it may be replaced by, for example, 'Tape022', but that would still be the 'Monday tape'.

Daily differential
We recommend that you keep four daily differential backup sets for Monday to Thursday on four different tapes. The default overwrite time set for the Daily Differential Backups media is six days. Remember that this is measured from the time the last backup ended, not when it started. Thus Monday's tape cannot be overwritten again until the following Monday due to the six day overwrite protection period.

It is worth noting that an append protection period is not set by default (i.e. the tapes are always append able) which means that any daily differential tape left in the drive could be appended to night after night. This will reduce the need to swap tapes but again this does not offer any protection against physical disaster and increases the amount of data that will be lost if there is an issue with that one tape.

Action: Change the daily differential tape(s) every day and rotate all four tapes (or sets of tapes) in turn.

Weekly full
We recommend that you execute weekly full backups to be used on successive Fridays (Friday1, Friday2, etc.) on four different tapes or sets of tapes.

The only way to fully recover a server to its most recent state is with the most recent full backup plus the most recent differential. As soon as the weekly full backup is complete, the tape(s) should be taken to a safe location far away from the servers and backup unit to protect them in case fire/flood/theft causes loss of servers or backup units. They should not be returned to the autoloader until Friday of the fourth week after they were last used. The default overwrite protection period is eight days which means that if Friday1 tapes were used in Friday3, they could be overwritten which is probably undesirable.

Action: Change the weekly full backup tapes every Monday and keep them out of the autoloader until the Friday they are required.

Spare/scratch tapes
Finally, it is prudent to keep at least one spare/scratch tape in the autoloader so that should there be any issues with the intended tape, the backup is not lost because the system will default to using this tape from that point in the backup on. The system will show an alert to make you aware of this issue so it can be investigated to understand the extent of the failure.