Re: Ramifications of dump cycle and number of tapes choices

On Mon, Jan 12, 2004 at 10:31:48PM -0500, Eric Siegerman wrote:
> On Mon, Jan 12, 2004 at 06:56:25PM -0600, Fran Fabrizio wrote:
> > [Assuming dumpcycle=7, runspercycle=7, runtapes=1, tapecycle=33:]
> > Are the following statements correct?
> > 
> > 1. We will have a full dump of any given partition somewhere on the most
> > recent 7 tapes
> 
> Yes.  As you've figured out, precisely where is up to Amanda.
> 

Just a slight revision.

In ANY seven consecutive tapes there should be AT LEAST one full dump
of each disk list entry.

The reason for the "at least" is that amanda tries to balance the
amount of tape used daily.  To do so it may "promote" a full dump
before it is needed according to the dumpcycle.

For example, here is a part of the output of amoverview for a config
with a dumpcycle of 7 and a runspercycle of 6.  Note /var sometimes gets
two full dumps in a row, others more frequently than every seventh day.


        date   12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 01 01 01
  host  disk   16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 01 02 03

  butch /       1  1  1  0  1     1  1  1  1  0  1     1  1  0  1  1  1
  butch /opt    1  1  1  0  1     1  1  1  1  0  1     1  1  1  1  0  1
  butch /var    1  1  1  0  1     2  0  0  1  2  2     2  0  1  1  2  2
  butch /img          0                    0                    0
  butch /u      1  1  1  1  1     0  1  1  1  0  1     1  1  1  0  1  1
  butch /u2     1  0  1  1  1     1  1  0  1  1  1     1  1  0  1  1  1
  butch /w      1  1  1  1  1     0  1  1  1  0  1     1  1  1  1  0  1
  butch /w2     1  1  1  1  1     0  1  1  1  0  1     1  1  1  1  0  1
  butch /w3              0                    0                    0

The ones without incrementals are specified that way in the disklist.

Also, other sites, with different data usage patterns, will have other
experiences, but I seldom see any dump levels > 2.  Thus, for a small set
of files, generally a restore only takes a single, maybe two tapes.  A
major restore might take three tapes.

-- 
Jon H. LaBadie                  jon AT jgcomp DOT com
 JG Computing
 4455 Province Line Road        (609) 252-0159
 Princeton, NJ  08540-4322      (609) 683-7220 (fax)