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

David Israelsson david at israelsson.org
Fri Aug 19 18:32:35 GMT 2005

Ilari Laitinen <ilari.laitinen at iki.fi> writes:

> 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?
I have asked myself the same question, why is the 3 2 5 4 6 5 9 8 9 9
... considered a good algorithm for storing backups?  We will get
exactly the same result by storing the dumps like 2 2 3 3 4 4 5 5 ...

I did ask this question elsewhere, and got the answer that it is
likely that somebody got it slightly wrong when rewriting some ancient
dump man page (of course I cannot find that man page right now).  The
algorithm describes labels on the tapes and which tapes to keep for
how long time, rather than dump levels.  This makes sense to me, can
someone supply a link to the man page I am talking about?

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