[BBLISA] Definition of dump levels?

[John Orthoefer]

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

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     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.