Customer backs up an AT&T SAP R/3 database with the Backint API client
using multiple concurrent sessions (client is a 8 processor CPU and
FDDI network).
Because the whole backup must fit on a disk storage pool, client
compression is switched on. The compression rate is very high.
The compressed files need only 25 % of the original space.
The files to be backed up are large database files.

We found the following problem :
When the client starts to transfer such a big file, the server
seems to reserve disk pool space in the size of the original
client file. When all 8 sessions want to start the transfer,
there is not enough space on the server side to hold all the
client files in their original size. This results in media-wait
conditions for some of the sessions. When the first sessions has
ended transferring their files that need actually much less space
because of the compression rate, the sessions in the media-wait
can reserve the requested server space and begin transferring
files.
So the problem is : the server storage is large enough
to hold all client files in compressed form but not large enough
to temporary reserve space for uncompressed files.
So the possible level of parallelism is reduced in this
installation.

Is there any way to solve this problem ?

Frank Hoehnel
IBM Dresden/Germany