CA Dynam for VSE User Guide

Releasing Unused Disk Space
Truncating Files
SD Files
For SD data files, CA Dynam/D performs truncation automatically by default.
You can suppress truncation by overriding the default for a given SD file.
Simply specify option code N for No truncate in the DLBL statement, as
follows:
// JOB DYNAM SD FILE
// DLBL SYMBOL,'DISK.FILE(N)',10,SD
// EXTENT SYS008,POOL01,1,0,1,100
// EXEC PROGRAM
CADD002I ALLOCATED FILE=SYMBOL SYS008=203 SYSWK1 X=0/19/100
In this example, the file is not truncated in EXTENT size to the amount of disk
storage actually utilized. The corresponding VTOC entry for this file remains
unmodified.
ISAM Files
For ISAM files, you can truncate the specified prime EXTENT by specifying
option code T in the DLBL statement.
Sequential Work Files
To perform truncation on sequential work files, you must specify option T on
the DLBL statement.
FBA DASD Files
Truncation will take place on FBA DASD in even multiples of 8 physical blocks
(512 bytes each physical block).
For example, if a file were to be created with an allocation of 160 blocks, and
only 147 blocks were used, the file would be truncated to block 152 rather
than 147. This restriction allows CA Dynam/D to control allocations on these
volumes with a bit map, greatly reducing system overhead.
CKD DASD Files
Truncation on CKD DASD will take place to the track following the last record
of EOF.
Chapter 4: Disk File Management 4–41