In <bitnet.adsm-l%ADSM-L%96012208130927 AT VM.MARIST DOT EDU>, koopmac AT 
hoogovens.e-mail DOT com (Kees Koopman) writes:
>---- Mail Item Text Follows
>subject: number of backupversions
>
>Folks,
>
>Does anyone have deeper thougths about the number of versions of client-
>files that should be maintained on the server as the default.
>We use 3 just because it sounds pretty save.
>
>But from the point of view of backup, one should say that 1 version would
>be sufficient. (We use ADSM V2 with copy storage pools).
>Keeping 1 version would, of course, save a  lot of DB and stgpool space,
>but, what would be the impact from other point of view, like risk
>management?
>
>Any ideas about this would be appreciated,
>
>Kees Koopman
>Hoogovens Groep BV
>Netherlands

 We keep 6 versions, with an age limit of 366 days.  These values were chosen
because that is what we do with MVS datasets backed up by DFSMS/hsm.  If the
version 2 client feature of from/to date restore were enhanced to filter out
deleted files, thereby producing a reliable 'point-in-time' restore
function, I would raise the versions to 33 and advertise to my users 'one
month PIT'.

 You can get a feel for how many inactive versions there are by doing exports
with preview=yes.  Randomly select some nodes and issue these 2 commands for
each node -

 export node <nodename> filedata=backupactive preview=yes
 export node <nodename> filedata=backup       preview=yes

The difference between the 2 will be the number of inactive versions.
Export has been thru some drastic changes, and depending on your server
level, these commands may be horrible pigs, but if you are one the latest
level they should be ok.

I did this for 10 nodes and on average half of the files are inactive versions.

Bill Colwell
C. S. Draper Lab
Email: BColwell AT draper DOT com
Voice: 617-258-1550