Item X: Create differential backups from X-th last full backup for better
redundancy
Origin: Jan Moennich
Date: 25 Mai 2007
Status: Nothing found
What: I'd like to have a differential backup, which backs up relative to
the second or third last
full backup instead of only the last full backup.
Eg. I made a full backup on 1 May, 8 May and 15 May, and make
daily differential backup.
On the 17th May all files should be backed up which changed
after 8th May - not the 15th.
Why:
We want to have every file older than two days redundant on at
least two tapes even with
differential backup.
We backup our files every week with a full backup. Daily we make a
differential backup.
If the last full backup tape is broken, we can't restore the last
differential backup completely.
With this features, every files (which is two days old) is always
stored on two tapes. For every
differential backup exists two valid full backup tapes.
Notes:
For a transparent configuration I would suggest an configuration
option "Ignore Previous Backups=n",
which will ignore the last n successfull previous backups for
looking for the last full backup.
Default (or current implemention) is 0, which simply searchs for
the last full backup.
If only the first full backup is made, the next differential
backup won't find a valid full backup,
so ist upgraded to the full backup. This is correct - after
initiation of a new backup cycle we want
to have at least two full backup for redundancy.
Maybe this is also sensefull for the incremental backup. Even the
last fullbackup can be lost to
restore the current state. Additional on a restore only half of
incremental backup have to be restored.
Alternatively an option "File Redundancy=m" where m is the count
of tolerated discs. If m=2, every file
change is stored in two subsequent backup. This is the same as
"Ignore Previous Backups=m-1".
Best regards
Jan Moennich
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