On Wed, Sep 28, 2005 at 12:03:52PM -0400, Bernard_Wu AT NCCI DOT COM wrote:
> Hi Graeme,
> By differential, I mean accumulating all the daily incremental backups into
> one backup tape.  I think the way it works is something like this:
> On Sun take a level 0 backup ( Full backup )
> On Mon take an incremental ( files that changed since the last backup ) -
> level 1
> On Tues, the backup should contain all the Monday's changes and Tuesday's
> changes.  - should be level 1 and level 2
> On Wed, the backup should contaon Monday's, Tuesday's and Wednesday's
> changes. - level 1, level 2 and level 3
> And so on and so forth.
> Thus on Saturday, the backup tape should contain all of Monday's,
> Tuesday's, Wednesday's ...... and Saturday's changes.
> 
> Something akin to using concatanete with tar, where the new changed files
> are simply added to the end of the tape.
> Don't know if this can be done with amanda.

That is basically what dump and tar's "levels" do.  Except they backup
everything from the previous lower number level.  So if amanda stays at
level 1 on Monday/Tuesday/Wednesday/... each dump has all the changes.
If it shifts to a higher number level, eg 2, then the dump is all the
changes since the last level 1.  A prime objective in this scheme is
to minimize the number of tapes needed to recover for a specific date.

The level changes are not always up.  Sometimes after switching to a
level 2 or higher, amanda will go back down a level or two.  In my
environment I almost never see a level 3, and only some level 2s.
So basically amanda is doing on my systems what you seek.

You also have some control over amanda's decision making for level
changes.  There are at least two parameters (I don't recall the
names for sure) that affect this.  One is the minimum time amanda
can stay at a level once it changes to that level.  The other is
how much of a savings in dump size must accompany a level change.
While your control may not be absolute, by proper setting of these
parameters you probably can get amanda to stay at level 1 between
full dumps.

Amanda does not append to tapes, so they won't all be on the same
tape.  Unless you let them collect on the holding disk and only
flush weekly (assuming 7 day dumpcycle).

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