Backup Levels
Backup levels come from the architecture of the UNIX dump
program. Each backup level is defined by a timestamp in the dumpdates
(or amandadates) file, which is structured as:
filesystem level timestamp
This tells when the last backup at each level was done. A Level 0
backup always backs up the complete disk, while a Level 1 backup copies
all the files and directories changed since the last Level 0. A Level
2 backup copies all the files and directories changed since the last
Level 1.
Therefore, to perform differential backups, you would use only
Levels 0 and 1, while to perform traditional 5-day incrementals
with weekly full backups, you would use a cycle of: 0,1,2,3,4,5,0.
Amanda follows a mix of strategies that enables it to use incremental
backups by bumping the tape level when the tape space to be saved
is significant, but also provide redundancy by keeping multiple
backups from the same level in the course of a single dumpcycle.
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