On Mon, Jan 06, 2003 at 01:29:09PM -0600, donald.ritchey AT exeloncorp DOT com 
wrote:
> Suggest that you consider setting up a dump-cycle of 1 week, with a tape 
> cycle of three weeks (5 tapes/15 tapes for weekdays only, 7/21 tapes for
> seven days-per-week cycles).  This will permit you to send out a complete 
> set of backup tapes once per week (for example, sending out the previous 
> weeks tapes on Monday) and getting back the set of tapes from two weeks 
> ago in exchange.  You then start reusing the three week-old tapes for the 
> current week.  You will need to have three sets of tapes, in case it takes 
> more than a day to exchange the tapes with your offsite repository.
> 
> Week    In-Use   Off-Site    To-Be-Reused
> 
>   1       Set3     Set2        Set1
>   2       Set1     Set3        Set2
>   3       Set2     Set1        Set3
>   4       Set3     Set2        Set1
> ....
> 
> Because of the one-week dumpcycle, you will always have a complete set of 
> dumps of each file system in the off-site tape set.  It will grow 
> increasingly out-of-date during the week, but storing your local collection
> of tapes in a fire-resistant vault should reduce your risks to an 
> acceptable level.
> 

A slight variation of this is a 4th set.  You may have a need to recover
very recent files and a need to keep a set off site.  By not rotating
off-site until a set has aged a week, you can keep the most recent set
in-house at the cost of a week's older set off-site.

-- 
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)