SAP Note 19909 - Setting compress_cmd for compress = only

Symptom:

Despite the fact that init.sap tape_size parameter was defined correctly (see Note 8707) and a dummy compression run was carried out (compress = only or -k only), cpio reaches the physical end of the tape.
cpio messages:
End of Medium ... , End of volume ... , End of Volume ...
Can't open /dev/tty to prompt for more media.
This can cause termination of the backup.

Cause and prerequisites

The compression rates determined by the dummy compression run do not correspond exactly to the hardware compression rates. This results in an incorrect distribution of the data for backup to the tapes.

Solution
If you carry out the compression with parameter compress = only or the -k option, SAP recommends using the option "-b 12" of the compress commmand in the definition of init.sap parameter compress_cmd, for example:
compress_cmd = "compress -b 12 -c $ > $"
The compression rates determined in this manner are much closer to the actual hardware compression rates, and therefore enable optimal file distribution and data media utilization.
This setting shortens the compression time.
Caution:
As of SAP Release 4.0 you should use the following command under Windows NT:
compress_cmd = "mkszip -l 0 -c $ > $"