First, you aren't really doing what you think you're doing: providing the 
ability to restore data back to any point in the previous 90 days.  You get 
seven days for a file that changes every day.

Steve is right: should probably do something like verexists=unlimited and 
retextra=21.  That way if you do a backup more than once a day you can still 
get 21 days worth of restores.

This boils down to how many files really change 21 times in 21 days.  Most 
files won't do that.  Large things, like SQL and Exchange databases will.  But 
you wouldn't really want to restore your SQL database back 21 days in any 
event.  How would you get back to scratch?  You couldn't.  So keeping these 
types of things for shorter periods makes more sense.

Anecdotally, my experience has been that increasing/reducing the numbers does 
not generally result in a ton more storage consumed/saved as most files are 
created and then never changed (or deleted).  They get backed up the one time 
and then live until they are deleted and retonly is reached.

I would definitely get to the 21/21 soon, though, as your user's expectations 
are probably different from what you're providing!

Kelly Lipp
CTO
STORServer, Inc.
485-B Elkton Drive
Colorado Springs, CO 80907
719-266-8777 x7105
www.storserver.com


-----Original Message-----
From: ADSM: Dist Stor Manager [mailto:ADSM-L AT VM.MARIST DOT EDU] On Behalf Of 
Steven Harris
Sent: Wednesday, March 18, 2009 3:24 PM
To: ADSM-L AT VM.MARIST DOT EDU
Subject: Re: [ADSM-L] Calculating Change in Backup Environment

Dennis,

FWIW, I don't like a N days/N versions strategy.  It can have unexpected
side effects.

N Days/unlimited versions has more predictable behaviour and also is more
efficient at expiry time.

Regards

Steve.

Steven Harris
TSM Admin, Sydney Australia




             "Dennis, Melburn
             (IT Solutions
             US)"                                                       To
             <melburn.dennis@S         ADSM-L AT VM.MARIST DOT EDU
             IEMENS.COM>                                                cc
             Sent by: "ADSM:
             Dist Stor                                             Subject
             Manager"                  [ADSM-L] Calculating Change in
             <[email protected]         Backup Environment
             .EDU>


             18/03/2009 11:46
             PM


             Please respond to
             "ADSM: Dist Stor
                 Manager"
             <[email protected]
                   .EDU>






Currently, our backup environment employs a 90-day / 7 revision backup
policy.  My customer has come to me to find out how much our backup data
would grow or shrink if we went to a 21-day / 21-revision backup policy.
Have any of you out there experience requests like this before, and if
so, how were you able to get a reasonable guestimate of this.

Mel Dennis
Systems Engineer II

Siemens IT Solutions and Services, Inc.
Energy Data Center Operations
4400 Alafaya Trail
MC Q1-108
Orlando, FL 32826
Tel.: 407-736-2360
Mob: 321-356-9366
Fax: 407-243-0260
mailto:melburn.dennis AT siemens DOT com
www.usa.siemens.com/it-solutions