UNIT Usage

If your existing JCL specifies an esoteric or generic device name in the UNIT parameter for a non-system-managed data set, then make certain that it is defined on the system performing the allocation. Although the esoteric name is ignored for a system-managed data set, the esoteric must still exist for non-system-managed data sets, including DD DUMMY or DD DSN=NULLFILE statements that include the UNIT parameter.

An allocation which specifies a volume, unit, DISP=OLD or DISP=SHR, and omits a data set name, as shown in the example below, results in an allocation to the volume.

//DD1 DD VOL=SER=SMSVOL,UNIT=SYSDA,DISP=OLD
//DD1 DD VOL=SER=SMSVOL,UNIT=SYSDA,DISP=SHR

If the volume is not mounted, a mount message is issued to the operator console. This occurs regardless of whether a volser is defined to an SMS storage group or to an SMS dummy storage group.