Serialization of user data sets

The basis of DFSMShsm serialization for non-VSAM user data set processing on a single DFSMShsm host environment is the SYSDSN resource. Serialization of VSAM user data sets use both SYSDSN and SYSVSAM resources. DFSMShsm can explicitly request the SYSDSN resource or can obtain the SYSDSN resource via allocation of the data set. The SYSVSAM resource can be requested only during the open of the data set. Table 1 describes the serialization for user data sets as DFSMShsm processes them.

Table 1. Single DFSMShsm host Environment User Data Set Serialization
Function	Data Set Organization	Share Options	Serialization
Migration	All	—	Exclusive
Backup	VSAM	—	Exclusive Note: DFSMShsm does no explicit synchronization, but DFSMSdss does a shared enqueue on SYSDSN and an exclusive enqueue on SYSVSAM.
Backup	Non-VSAM	—	Shared

Exclusive control results in the correct level of control possible in the systems environment.

In a single DFSMShsm host environment, the preceding serialization is all that is needed. In a multiple DFSMShsm host environment, update protection must be extended to the other processors. That protection can be achieved with GRS or an equivalent cross-system enqueue product.