DS release unused storage space

DS Deallocate Space. The unused storage space belonging to a file (PAM pages that have been allocated, but not written to) is released:

FILE ..., SPACE=-99999.

DS [n] Deallocate Space. The unused PAM pages allocated to the file will be released up to a multiple of n pages (0 <= n <= 999).

DS will cause all pages down to the minimum allocation to be released for files which have not yet been opened, but for which a /FILE command has been issued.

DS0 will cause all pages reserved by the file to be released completely, leaving the file without any space allocation.