You can specify the write validity check option in the DCB parameter of the DD statement, the dynamic allocation text units, or the DCB macro. After a block is transferred from main to auxiliary storage, the system reads the stored block (without data transfer) and, by testing for a data check from the I/O device, verifies that the block was written correctly. Be aware that the write validity check process requires an additional revolution of the device for each block. If the system detects any errors, it starts its standard error recovery procedure.

For buffered tape devices, the write validity check option delays the device end interrupt until the data is physically on tape. When you use the write validity check option, you get none of the performance benefits of buffering and the average data transfer rate is much less.

Rule: OPTCD=W is ignored for PDSEs and for extended format data sets.