dump(8), incremental backups, Tower of Hanoi sequence, don't get it

Ilari Laitinen ilari.laitinen at iki.fi
Fri Aug 19 14:14:04 GMT 2005


Lately I have been getting more and more worried about data on my
FreeBSD box at home. I am forming a "real" small-scale backup policy
with two different big USB harddrives (yet to buy) storing regular
incremental backups (yet to figure out). The idea is to have those
harddrives mirror each other for extra security.

Handbook reads dump(8) is the best backup program there is. So I am
giving it a try - only to find out that I don't understand at all the
meaning of that modified Tower of Hanoi algorithm descibed in the
manual page and elsewhere. The manual page says it is "an efficient
method of staggering incremental dumps to minimize the number of
tapes." I just don't get the picture here.

So, could somebody please give an idiot-proof explanation why "3 2 5
4 7 6 9 8 9 9" is such a tape-number-minimizing dump level sequence
(with helpful examples, if at all possible)? How does it work?

Am I relatively safe doing level 0 dump every two months and
increasing dump level for weekly backups like the following, given
two separate harddrives storing them?

Date        Dump level
2005-09-01  0
2005-09-08  1
2005-09-15  2
2005-10-27  8
2005-11-03  0


Ilari Laitinen,
    dumb dump newbie lost in this big world of ever-so-failing disks

Ilari Laitinen - ilari.laitinen at iki.fi - http://iki.fi/ilari.laitinen/
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