Level 0 is everything (aka a full)
Levels 1-9 do everything since the last "lower level". So a 1 does
everything since the last zero, a 2 does everything since the last 0 or 1...
Most people today do 0/9s Zeros once month/quarter/semester, and 9s
till the next zero. That allows you to use 2 recoveries to get
everything back (the Full and the last incremental.)
However, there is an old system which is/was documented in the dump man
page (which also explains dump levels.) Call the tower of Hanoi
sequence.
johno
-------------------------------
In the event of a catastrophic disk event, the time required to restore
all the necessary backup tapes or files to disk can be kept to a
minimum
by staggering the incremental dumps. An efficient method of staggering
incremental dumps to minimize the number of tapes follows:
o Always start with a level 0 backup, for example:
/sbin/dump -0u -f /dev/nrst1 /usr/src
This should be done at set intervals, say once a month or
once
every two months, and on a set of fresh tapes that is saved
forever.
o After a level 0, dumps of active file systems are taken on a
daily basis, using a modified Tower of Hanoi algorithm, with
this sequence of dump levels:
3 2 5 4 7 6 9 8 9 9 ...
For the daily dumps, it should be possible to use a fixed
num-
ber of tapes for each day, used on a weekly basis. Each
week,
a level 1 dump is taken, and the daily Hanoi sequence repeats
beginning with 3. For weekly dumps, another fixed set of
tapes
per dumped file system is used, also on a cyclical basis.
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