Hi Stefan,

----- Original Message -----
From: "Stefan G. Weichinger" <monitor AT oops.co DOT at>
To: amanda-users AT amanda DOT org
Subject: Re: Meaning of "bump"
Date: Sat, 15 Jan 2005 12:08:31 +0100

> OK, it says:
> 
> > The minimum savings required to trigger an automatic bump from one
> > incremental level to the next. If AMANDA determines that the next
> > higher backup level will be this much smaller than the current
> > level, it will do the next level.
> 
> I see that bump->bump-thing ... will correct that.

yes, that's what i meant
 
> The basic goal of using these parameters is avoiding too much
> incremental backups happening too fast.
> 
> As it gets harder to restore from a backup-set with lev4 or similar as
> you have to use 5 tapes to get your full data back, you want to avoid
> lev4 and just go to lev2 or lev3 ...
> 
> So you want to get some benefit from BUMPING to lev2 (which actually
> means the switch from level n to level n+1) after you are already on
> lev1, and this benefit should be saving tapespace because that lev2
> backup is smaller than the lev1.

that's exactly what i would like to read in the docs (Bumping means switching 
backup levels or so).  
 
> Now read again: "If AMANDA determines that the next higher backup level
> will be this much smaller than the current level, it will do the next
> level."

i understand this in the context you gave - but i was completely unsure about 
it when i read it for the first time.
please don't take it too serious - i simply think that people enjoy reading the 
docs more when this is clearer.  

> If size_of_lev(n+1) - size_of_lev(n) > bumpsize, then AMANDA decides
> to do the lev(n+1), because the savings in space are worth it.
> 
> Not enough with this, there is also bumpmult !
> 
> Actually it's:
> 
> threshold = bumpsize * bumpmult^(level-1)
> 
> This introduces a somewhat exponential behavior, bumping from lev2 to
> lev3 should be harder than bumping from lev1 to lev2, as you want to
> avoid high backup-levels.
> 
> There is also "bumpdays" to keep the lev down as well.
> 
> ---
> 
> This as a quick-n-dirty-explanation, hope this helps.

perfectly - that's what i was looking for :-)

thanks,
Kai