Storing Backups and Media Life Expectancy

Finding a good way to store backups is almost as important as setting up a schedule to create them. Backups, installation media and boot disks should be stored in place where only authorized people have access to them. In order to make restorations as painless as possible, backups need to be easy to get to and well labeled. Labeling includes clearly marking the tape itself as well as including a table of contents file so that individual files on the tape can be found easily. In sites where several people share responsibility for making backups or a number of different commands are used to create backups, the label should also include the command used to create the backup. The label is also an ideal place to keep a running tally of how many times the media has been used and how old it is.

Most backup media are sensitive to heat, humidity, direct sunlight and dust. So a cool, dry storage area is best. Ideally media should be stored in an environment with a temperature of 62-75 degrees Fahrenheit at 40% humidity. Keeping backups in the same room as the system may be convenient, but not the best idea. In a worst case scenario where damage is done to the room that houses the system, the backup media may be destroyed also.

3. Backup media may be more sensitive to certain conditions than the system itself.

Making a copy of a level 0 backup, taken shortly after the system is set up, and storing it in a secure place off site is also a good idea. Ideally copies of full backups should also be stored off site in a fireproof, locked and environmentally controlled room. When creating a backup to be placed in long term storage it is best to use whatever media lasts the longest. RCDs (recordable CDs) have a much longer lifespan than tapes. So do optical disks.

4. What else can a level 0 backup, taken right after the system is set up, be used for?

For safety's sake all backups should be checked to verify that the media is readable. This can be done using the restore command to list the contents of the tape. Some backup utilities provide full verification of every file on the tape, but this is rare.

There are a couple things to consider in terms of backup media life expectancies. For long term archiving, changing technologies may result in the media becoming obsolete before it degrades and the information on it becomes unusable. Unfortunately there is no standard method for determining life expectancy of the media itself. Manufacturers will frequently give a recommendation on the number of times that the media can be reused as well as an estimated life expectancy. It is best to stick to the conservative side of these numbers. The physical lifetime of the media may be much longer than the amount of time it takes for the information on the media to degrade. The following is general estimate of how long backup media can to remain stable and usable.

Magnetic tape		1 year
Video tape		1-2 years
Magnetic disks		5-10 years
Optical disks		30 years
Write-once CDs		30+ years

Life expectancy and the number of times a tape can be reused depends on several factors beyond the quality of the tape itself. Wear on the magnetic coating, stretching of the ribbon, the storage environment and the alignment of the read/write heads on the tape drive can all affect the life expectancy of a tape. One way to reduce problems is to use a tape cleaning cartridge frequently as dirty tape heads can cause read/write errors. New tapes shed more oxide than older ones, so the heads should be cleaned more often when using new tapes.

For more optional information on the life expectancy of magnetic tapes see What Can Go Wrong with Magnetic Media?.