Thanks for the information especially about the difference between
"Sectors Wasted" and savable sectors.   When I do a LISTF,SAVABLE
it does say that over 16% of my disk space is savable.

Thanks!

  ---------------------------------------------------------------
  Barry Durand      "The opinions expressed in this
  Systems Engineer II    email are not necessarily the
  Gulf South Health Plans    opinions of my employer"
  [log in to unmask]
  ---------------------------------------------------------------

______________________________ Reply Separator _________________________________
Subject: Re: MPEX;XLTRIM and Image datasets
Author:  Ken Paul <[log in to unmask]>  at SMTP-PO
Date:    12/18/97 11:53 AM


Barry wrote:

>     After using the LISTF command with the SAVEABLE option on the
>     group which contained our production Image databases I discovered
>     that I may be able to recover about 15% disk space.  While I
>     would like to just go ahead and use the ALTFILE;XLTRIM command I
>     am a bit cautious about doing it.
>
>     I realize that XLTRIM will not change the file limit and I am
>     assuming it also won't change the capacity.  I am just cautious
>     about doing this on our production database with out any
>     guarantees.  Needless to say I will test it on our test database
>     (which is MUCH smaller) and will have a good backup before I do
>     it.
>
>     My questions are:
>     1. Has anyone done this before? (I would think someone has)
>     2. Are there any ill effects from this?
>     3. What are the dangers?
>     4. Were the benefits as good as expected?
>     5. Any other precautions I should take?
>     6. Is there a way I can get the sectors wasted per file (like the
>        DB option the LISTF command) on non-Image files?
>
>     Here is the general info:
>     MPE\iX version 5.0
>     MPEX version 2.5
>     Amisys version 8.?
>
>     Thanks to everyone for their help with this!

Barry et al.,

There is a BIG difference between MPEX savable disc space and the Wasted
Sectors reported by a LISTF,DB within MPEX.

I use the following command regularly on my systems to get back savable
disc space using MPEX:

ALTFILE @[log in to unmask]@(savable>0);XLTRIM;KEEPAMDATES

This command will only alter those files which have savable space so you
can see which files are being altered.  I have had no problems when using
this command over the years.  If MPEX does an XLTRIM on an IMAGE dataset (I
know it wont let you do a SQUEEZE to an IMAGE dataset), it will not have
any negative impact but I would be surprised if any IMAGE database showed a
lot of savable sectors as Lee has mentioned.

The LISTF,DB command shows WASTED SECTORS which tend to show more waste for
larger datasets as Barry has pointed out.  The only way to improve on this
is to try to reblock your dataset to use as much of the block as possible.
This waste is caused by the IMAGE requirement of rounding the MPE record
size to a multiple of 128 words.  Rarely do IMAGE blocks get used 100%.  As
the file becomes larger (has more MPE records) the wasted sectors becomes
larger.

Hope this helps someone,


+---------------+
|               |
|            r  |  Ken                             [log in to unmask]
|          e    |                           http://www.adager.com
|        g      |  Ken Paul                      Tel 208 726-9100
|      a        |  Customer Support              Fax 208 726-2822
|    d          |  Adager Corporation
|  A            |  Sun Valley, Idaho 83353-3000            U.S.A.
|               |
+---------------+