If you are appending data to existing log stream copies
by specifying the MOD keyword in the log stream copy job, you must change
the format of the log stream copy before you run the job using CICS® VR V4R3.
The format of the output log stream copy produced by the CICS VR log stream copy utility has changed from the CICS VR V2 format (RECFM=U, BLKSIZE=6000), to RECFM=VB and BLKSIZE=6144 in CICS VR V3 and CICS VR V4.