Tivoli Storage Manager (TSM) is a Full Back up Once and an incremental back up forever afterward. It is an index database that keeps track of changes and writes to information to a robotic tape library.
TSM backups are managed by policies. Each policy consists of multiple rules. Four rules are of interest with regard to file retention on tape. The rules for the Windows Server follow:
|1||7||# of versions (active + inactive) on tape|
|2||7||# of versions on tape when the file has been deleted from disk
(note rules #3 & #4 are factors here too!)
|3||30||# of days to retain an inactive version from the day it goes inactive|
|4||180||# of days to retain the only backup version when the file has been deleted from disk|
Some terminology is necessary to understand the rules. TSM refers to the version of a file on disk as the active version. All other versions are called inactive versions.
- If a file exists on disk, the active version will always be on tape. See rule #1.
- If you modify a file every single day, there will be one active version and six inactive versions on tape. See rule #1.
- If you modify a file for seven consecutive days and then never modify it again, there will be seven versions on tape for 30 days, six versions on tape after 31 days, five versions on tape after 32 days, four versions on tape after 33 days, three versions on tape after 34 days, two versions on tape after 35 days, and one version on tape thereafter. See rules #1 and #3.
- If you modify a file routinely once every 30 days, there will be just two versions on tape. See rules #1 and #3.
- If you delete a file, there will be at least one version on tape for 180 days. See rule #4. After 180 days, there will be no version on tape. Again, see rule #4. Also, it should be noted that there might be up to seven versions on tape for 30 days. In most cases, there will be less than seven versions on tape. Note this subtlety! See rules #2 and #3.