The data set compressed by AMATERSE (produced by PACK or SPACK) must be of fixed or fixed-blocked record format (RECFM) with a record length (LRECL) of 1024 and any legal block size (BLKSIZE). These values do not have to be specified explicitly on the DD statement.
The data set restored by AMATERSE (produced by UNPACK) must match the original RECFM and LRECL. Leave the DCB information off the DD statement for AMATERSE program to set it up. If it unpacks to an already existing data set then the DCB parameters are checked for compatibility. RECFM must be the same in all cases except for Variable to Undefined and Undefined to Variable. If you specify the DCB parameters to force data that was originally variable (V) format into undefined (U) format, or conversely, a warning message is written and the operation is performed.