Besides having caching turned on that Betsy Moir just mentioned, another use
of space is when backup sessions are active.  This is something that I came
across a week or two ago and an append to the list resulted an a reply from
an ADSM/TSM developer.  I was seeing the same type of thing that you are and
appended with the subject "ANR0534W Size estimate exceeded" on September 24.
The net of the response from David Bohm, a developer, is that disk pool
space is used, or at least allocated, while a backup session is active in
anticipation of the requirements of the backup session.  It will show up as
percent utilized and not percent migratable.

Jim Bohnsack
Raytheon Systems Co

> ----------
> From:         Dana Mitchell;[SMTP:Dana.Mitchell AT ING-DM DOT COM]
> Reply To:     ADSM: Dist Stor Manager
> Sent:         Monday, October 11, 1999 9:53 AM
> To:   ADSM-L AT VM.MARIST DOT EDU
> Subject:      Percent utilized greater than Percent migratable
>
> ---------------------- Information from the mail header
> -----------------------
> Sender:       "ADSM: Dist Stor Manager" <ADSM-L AT VM.MARIST DOT EDU>
> Poster:       "Dana Mitchell;" <Dana.Mitchell AT ING-DM DOT COM>
> Subject:      Percent utilized greater than Percent migratable
> --------------------------------------------------------------------------
> -----
>
> Hello
>
> I am running 3.1.2.40 server on OS/390 and noticed my percent utilized is
> much larger than percent migratable.  According to the manual this
> difference is due to the amount of uncommitted data in the backup pool.  I
> can't explain the difference though.  Example, I have a diskpool of about
> 85GB.  Currently percent utilized is 75% and percent migratable is 53%.
> The difference of 22% of 85GB is about 18GB.  Where could this 18GB be?  I
> have two NT notes servers clients running each with 5GB bytes received so
> I
> could maybe believe 10GB uncommitted, but where could the other 8GB be?
>
> TIA
>
> Dana Mitchell
>