Fileshare is a client/server file handler, supplied as part of Enterprise Server. When you configure an enterprise server to use Fileshare, you are making the enterprise server a Fileshare client, so that some or all file I/O requests coming from applications running in that enterprise server will be handled by a Fileshare server.
Fileshare can be used for CICS applications, files accessed by JCL, and even the catalog itself. It can also access data files on other systems running on the same network as the machine running Enterprise Server. These Fileshare files can still be accessed by other applications at the same time.
Although its name implies file sharing, the major benefit of Fileshare in Enterprise Server is when used with CICS, as it provides transactional access support to data files using the COMMIT and ROLLBACK verbs or EXEC CICS SYNCPOINT. Without using Fileshare, there is no CICS transactional behavior in Enterprise Server.
Fileshare also provides rollforward and rollback recovery to ensure the integrity of your files in the event of a system failure.