From: utzoo!decvax!ittvax!shp
Newsgroups: net.unix-wizards
Title: Re: dump and restor
Article-I.D.: ittvax.514
Posted: Fri Nov 12 14:26:06 1982
Received: Mon Nov 15 03:06:01 1982
References: micomvax.106

The Tower of Hanoi is used to keep the number of tapes needed for a complete
restore to an abosolute minimum.  You have to really understand the concept
of dump levels.  From dump(8):

	0-9 This number is the 'dump level'.  All files modified since the
	    last date stored in the file /etc/dumpdates for the same
	    filesystem at *lesser* levels will be dumped.  If no ...

Consider the following dump cycle:

day	01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20 21 22 23

level   0  3  2  5  4  7  6  9  8  9  9  1  3  2  5  4  7  6  9  8  9  9  0


On day 01 a zero (complete) dump is performed.  On 02, a level 3 dumps all
files modified since day 01.  The level 2 dumps all file modified since
day 01.  If you had to restore now you'd only need the tape sets from day 01
and 03.  On day 04 you do a level 5 dump.  This dump only dumps files modified
since day 03.  And so on ...

After dump on day 12, the system can be restored using the 0 and 1 level tape
sets.

The Tower of Hanoi minimizes:

	-	number of tape sets needed to fully recover
	-	the average number of files dumped daily



		- sam praul
		  ...decvax!ittvax!shp