Assembly / HLASM · Message ID
What does IEC023I Block Count Mismatch Message mean in Assembly / HLASM?
Generated during end-of-volume processing on tape when the block count recorded in the trailer label doesn't match what the DCB counted, or when the dataset name found on a subsequent volume of a multi-volume set doesn't match what was expected — along with tape I/O errors during EOV itself, extended-format/large-block handling issues, and DEB (Data Extent Block) lock conflicts. The return code in the message (04 through 30) distinguishes which of these actually occurred.
Generated during end-of-volume processing on tape when the block count recorded in the trailer label doesn't match what the DCB counted, or when the dataset name found on a subsequent volume of a multi-volume set doesn't match what was expected — along with tape I/O errors during EOV itself, extended-format/large-block handling issues, and DEB (Data Extent Block) lock conflicts. The return code in the message (04 through 30) distinguishes which of these actually occurred.
Verify the correct tape volumes were mounted in the right sequence for a multi-volume dataset, and treat a block-count mismatch as a possible sign of data corruption on that reel until the data has been validated. Check the specific return code before assuming a label/block-count issue, since several of the documented causes point to a tape I/O problem or a DEB lock conflict instead.