Hello,

I was trying to think through what we want our dump cycle and total
number of tapes to be, and I realized that I wasn't quite clear on some
things.

We have a changer with a capacity of 33 tapes.  We have Amanda
configured for a 7 day dump cycle, backups every night.  Our backups
currently use only 1 tape per run.  I'm trying to figure out what our
"minimum service level guarantee" would be if we used 33 tapes in our
changer and we assume that it's 1 tape per run.

Are the following statements correct?

1. We will have a full dump of any given partition somewhere on the most
recent 7 tapes and that to restore a file to any given date in the past
7 days would take at most 7 tapes/steps but on average 3.5 tapes/steps.

2. We can retrieve a file as it existed on any date in the past 27 days,
and possibly as it existed on days 28-33 (with Amanda shifting around
full dumps, you never know how old the oldest full dump available will
be, but you will know that it will be at least 27 days old, right?  My
thinking is that to retore any file you need to start with a full dump,
and with 33 tapes and a 7 day cycle, if day 34 was a full dump, days 33,
32, 31, 30, 29, and 28 could have been incrementals before a forced full
on 27.  Hence, it seems you are guaranteed to be able to retrieve any
file as it existed 27 or less days ago.

I don't really want to start using Amanda in the manner of CVS where I
start retrieving older versions of files where newer ones exist on a
regular basis, but I would like to know the boundaries for when we do
need to do this. 

Thanks,
Fran

-- 

Fran Fabrizio
Senior Systems Analyst
Department of Computer and Information Sciences
University of Alabama - Birmingham
fran AT cis.uab DOT edu
(205) 934-0653