When your program is in write mode, the system will try to ensure that your data is safe on the medium in each of the following circumstances:

• The program switches to another volume to continue writing.
• The data set is closed.

If the system's volume-switching function or close function detects a data loss, it issues an ABEND.

Issuing a BSAM CHECK macro or EXCP WAIT macro ensures that the data has been sent to the device. Whether it is safe on the medium depends on the type of device and data set, and on the guaranteed synchronous write option in the storage class. This storage class option affects only PDSEs. You can use the SYNCDEV macro to ensure synchronization, but the performance might not be up to your installation's standards.