It sounds like you are not using Dynamic Volume Count or Partial Space release.

Dynamic volume count allocates the 1st extent on the 1st volume and dynamically 
adds volumes to the list, up to the architectural max of 59. It is not 
necessary to specify (for example) 10 volumes in JCL. It is specified in the 
DATACLAS assigned to the dataset.

Partial Space Release will release unused space with a sequential file at dfHSM 
Primary Space Management time. This is specified in the MGMTCLAS assigned to 
the dataset.

You might also check and see if the Guaranteed Space is specified in the 
STORCLAS assigned to this dataset...

Check the fine manuals for dfSMS or the online help for further details.

HTH,

<snip>
I have an application that may have to write DASD files very variable in size. 
These files are dynamically allocated as SMS managed files (using DALSTCL, 
DALMGCL and DALDACL) and with text unit DALRLSE (equivalent of the RLSE JCL 
keyword) so that unused space is released from the allocation when closing the 
file after writing it.

This works well with mono-volume data sets, but is it possible to make it work 
for multi-volume data sets too ??

After testing a bit, it looks like:
-       At the time of allocation , the primary space amount is allocated on 
EACH of the volumes if the volume count (DALVLCNT) is greater than 1.
-       At the time of CLOSE,  the unused space is released on the current 
volume (the last one that was written to). But, and this is my problem, the 
allocations on the (unused) next volume(s) if any, are NOT freed !!!

Is it possible to specify something (in SMS ?) so that it would free ALL unused 
space ?
</snip>

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