On Fri, Oct 03, 2003 at 04:00:16PM -0700, S. Keel wrote:
> I'd like to bouce this off you all to make sure that I'm understanding
> things correctly.
> 
> Lets say that my total data to be backed up is 83.5GB, and from some
> initial trial runs, I've achieved at least 50% compression, bringing that
> down to 41.75GB.
> 
> I've set my dumpcycle to 1 week, and runs per cycle to 5 so that the
> backup runs only on weekdays (when I'm available to deal with possible
> errors, etc.).
> 
> Since my tapes are 20/40GB, given the compression that I'm getting, I
> should only need 3 tapes for the entire dump cycle, correct?  2 tapes to
> handle the dump cycle, and one extra for security.
> 
> If I'm understanding how Amanda works, during the course of the dump
> cycle, she performs a full backup of each disk in the disklist.  She uses
> her keen wisdom in determining on which days she does a full backup of a
> particular disk, and on which days she does an incremental; nonetheless,
> by the end of the dump cycle, she will have consumed a total of 41.75GB of
> tape.
> 
> Does this all sound right to you?


No, it does not.

What you are missing is that amanda never writes multiple
amdump runs on a single tape.  (well, amflush is different)

What you really need is a MINIMUM, absolute minimum, of
runspercycle + 1 tape.  This is assuming that no single
days run takes more than one tape.  A safer number of
tapes is 2 times runspercycle and maybe +1.

You do not want to be in the situation where one dump
of /xyz might be an incremental and over write your
last full dump of /xyz.  Because unless you have a
full dump of a disk to start with, you can't restore.

-- 
Jon H. LaBadie                  jon AT jgcomp DOT com
 JG Computing
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