From: bsa@kf8nh.wariat.org (Brandon S. Allbery) Subject: Re: where is dump? Date: Sat, 14 Aug 1993 22:52:00 GMT
In article <CBrE6F.6AA@hip-hop.suvl.ca.us> dfox@hip-hop.suvl.ca.us (David Fox) writes:
>Also I don't really see the distinction between different dump levels in
>the dump utility (perhaps one can elaborate on this) - I see two different
>backup stategies, namely a full backup, and an incremental one, which is
>easily derivable from (for example) touching a file in /etc after the
>full backup, and using find -newer to get filenames modified since the
>last full backup.
When dump and restor were written and subsequently Berzerkeleyized, find
didn't understand -newer.
The other reason had to do with a "tower of Hanoi" (so called by the "dump"
manpage; actually, it was a geometric progression) backup schedule which
arranged for a series of progressively older tapes: at one tape per dump
level and the dump levels alternated according to a binary sequence (1, 2,
1, 3, 1, 2, 1, 4, 1, 2, 1, 3, 1, 2, 1, 5, ...) you get (assuming daily
backups):
1 week on 4 tapes
2 weeks on 5 tapes
4 weeks on 6 tapes
8 weeks on 7 tapes
16 weeks on 8 tapes
32 weeks on 9 tapes
64 weeks on 10 tapes, which is the limit.
Tape # N (starting from 1) corresponds to dump level 10-N, which is why 10
tapes is as high as you can go.
This can save your *ss if something from half a year ago needs to be restored
from tape for some reason. (It happened to me once.) But, from the same
period, keeping track of what tape/dump level to use on what day is a bit of
a problem, because days/weeks/months just don't fit into powers of 2 too well.
++Brandon
-- Brandon S. Allbery kf8nh@kf8nh.ampr.org bsa@kf8nh.wariat.org