DSNT504I UNLOAD DATA SET `ddname` BLOCKSIZE SET TO `nnnnn`.

Explanation

The block size for the SYSRECnn or SYSPUNCH data set was one of the following:

Not specified in the JCL
Set to zero in the JCL
Less than the required record length
Not an even multiple of the required record length

System action

DB2® sets the block size of the unload data set to the value specified in the message text.