Understanding dump levels

The dump command has the capacity to back up all files on a file system, or it can selectively back up only those files that have changed recently. The dump level parameter is used to specify this behavior. A dump level of 0 results in a full backup of all files on the file system. Specifying a higher number (1-9) backs up only those files that have been changed or added since the most recent dump of the same or lower dump level. I recommend you use dump levels to implement a full and incremental backup schedule similar to that shown in Table 13-4.

Table 13-4: Recommended dump Schedule

Day of Week

Dump Level

Sunday

Level 0 (full dump). Eject the tape when done.

Monday

Level 9 (incremental dump).

Tuesday

Level 8 (incremental dump).

Wednesday

Level 7 (incremental dump).

Thursday

Level 6 (incremental dump).

Friday

Level 5 (incremental dump).

Saturday

Level 4 (incremental dump).

Note that after the full backup on Sunday, a level 9 incremental dump is done the next day, and a successively

lower dump level is done each day after that. This results in all the files that have changed since Sunday being backed up on every single incremental backup. Each incremental backup is thus larger than the previous; the backup contains all of the files from the previous incremental backup plus any files that have changed since then. This may seem wasteful of storage space on the backup tape, but it will save a lot of time and effort should there be a need to restore the file system.

For example, let us imagine that your hard drive crashed on Friday. After replacing the hard drive, you can restore the entire file system in two steps: restore the full backup from the prior Sunday and then the most recent incremental backup from Thursday. We can do this because Thursday's backup contains all of the files from Monday, Tuesday, and Wednesday's tape as well as the files that changed after that. If the dump levels had progressed in positive order (level 1 for Monday, level 2 for Tuesday, and so on), all of the incremental backups would have to be restored in order to restore the file system to its most current state.

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