If the device supports buffered tape marks, the OPEN, EOV, and CLOSE functions take advantage of it when writing. This can save several seconds of real time. If the device does not support buffered tape marks, this option has no effect. Similarly this option has no effect on an older level of the system. SYNC=NONE might have an effect on other device types. This option does not affect the final tape mark written by the EOV function.

Specifying the option NONE can affect data integrity. If this option is in effect when making the transition to a new volume or when closing the data set, the system does not ensure that user data, tape marks, and data set labels are safely on the medium.

Use this option only under the following conditions:

• Your data is not important. For example, if it is test data, or you are measuring performance.
• Your program turns the option on before opening the DCB and turns the option off after the OPEN. This allows the OPEN to be much faster. If there is an I/O error while the data set labels or tape mark are being written, OPEN might not detect it, but it is reflected either while your program is writing or during CLOSE. If it is reflected while your program is writing, the system calls your program's SYNAD routine and if it is not available, the system issues an ABEND 001. If your data set is relatively small and the system does not detect the header label I/O error until CLOSE, CLOSE issues an ABEND if this option is still in effect. Your program can turn this option on or off at any time.
• Your program is writing multiple files on the tape and your program has a method of recovering the loss of multiple files. For example, your program might be designed to write multiple files and is not successful unless all the files are written. You should turn SYNC=NONE off before the last CLOSE or before the last OPEN.