The volume attribute list

In MVS™, each online device in the installation has a mount attribute and each mounted volume has a use attribute.

The mount attributes determine when the volume on that device should be removed. This information is needed when selecting a device and during step unallocation processing. The mount attributes are:

Permanently resident
Reserved
Removable.

The use attributes determine the type of nonspecific requests eligible to that volume. The use attributes are:

Public
Private
Storage.

Allocation routines use the volumes' mount and use attributes in selecting devices to satisfy allocation requests. Thoughtful selection of the use and mount attributes is important to the efficiency of your installation. For example, during allocation, data sets on volumes marked permanently resident or reserved are selected first because they require no serialization, thus minimizing processing time.

During system initialization, you can assign volumeattributes to direct access volumes by means of the volume attribute list. The volume attribute list is defined at IPL time using the VATLSTxx member of SYS1.PARMLIB.

After an IPL, you can assign volume attributes to both direct access and tape volumes using the MOUNT command. The USE= parameter on the MOUNT command defines the use attribute the volume is to have; a mount attribute of reserved is automatic. For the details of using the MOUNT command, see z/OS MVS System Commands.

When volumes are not specifically assigned a use attribute in the VATLSTxx member or in a MOUNT command, the system assigns a default. You can specify this default using the VATDEF statement in VATLSTxx. If you do not specify VATDEF, the system assigns a default of public. For details on including a volume attribute list in IEASYSxx,and on coding the VATLSTxx parmlib member itself, see z/OS MVS Initialization and Tuning Reference.