ISM_COMPRESSION worked on 9 and 10 IDS does not work on 11.50 or 11.70 IDS
Your having trouble getting backup compression to work with onbar and ISM. You've already set
the ISM_COMPRESSION environment variable to TRUE, but this doesn't seem to be working.
ISM_COMPRESSION was free on the earlier versions of the engine
Compression was introduced, along with repack and shrink, in 11.50.xC4. While repack and shrink may be used without charge on any edition, compression requires an additional license and can only be used with Ultimate Edition.