General rules and restrictions

The maximum unload record length is 32780, which occurs when the data set being unloaded has a block size of 32760.
Note that this is longer than the maximum permitted physical block length of 32760 bytes, so sometimes records must be spanned across physical blocks.

This number also exceeds the maximum LRECL allowed in a data set label. When the data set label LRECL is 32760, the assembled logical record may actually be longer.
When a record must be spanned across physical blocks, each block except the last must be completely filled.
The length of any unload data set physical record can never exceed the unload data set logical record length plus 4, even when the data set block size would allow a longer physical record.