Restrictions on UNIX Files

The following VSAM restrictions are associated with UNIX files:

Only ESDS is simulated.
No file sharing or buffer sharing is supported except for multiple readers and, of course, for a reader and a writer for FIFO.
STRNO > 1 is not supported.
Chained RPLs are not supported.
Shared resources is not supported.
Updated and backward processing is not supported.
Direct processing or POINT for FIFO and character special files are not supported.
There is no catalog support for UNIX files. The data set that contains the files might be cataloged.
Alternate indexes are not supported.
There is no support for JRNAD, UPAD, or the EXCEPTION exit.
There is no cross-memory support.
ERASE, VERIFY, and SHOWCAT are not supported.
Certain SHOWCB requests return dummy values.
Variable-length binary records do not retain record boundaries during conversion to a byte stream. During reading, each record, except the last, is assumed to be the maximum length. You can avoid this restriction by using FILEDATA=RECORD. The access method will add metadata in the file to define record boundaries.
To specify the maximum record size, code the LRECL keyword on the JCL DD statement, SVC 99, or TSO ALLOCATE. If not specified, the default is 32 767.
On return from a synchronous PUT or a CHECK associated with an asynchronous PUT, it is not guaranteed that data written has been synchronized to the output device. To ensure data synchronization, use ENDREQ, CLOSE, or CLOSE TYPE=T.
There is no CI (control interval) access (MACRF=CNV).