In BS2000, disks can always be utilized either as private disks or as public disks.
Prior to their first use the volumes must be initialized with the VOLIN utility routine. There will be written a volume serial number (up to 6 characters) to the standard volume label. This volume serial number (VSN) serves to distinguish private from public disks.
The VSN of a private disk is freely selectable, with the restriction that the name must not be the same as that of a public disk. The rules and possibilities for assigning a VSN for public disks are explained in the section "Pubset properties".
There are two possible applications for private disks:
DMS applications
The disk is reserved by one or more DMS applications.
By default, the allocation mode is defined as task-shareable. Task-exclusive allocation is effected by means of the user command SECURE-RESOURCE-ALLOCATION. The system allocation mode depends on the generation characteristics of the device on which the disk is mounted. With the operator command SET-DISK-PARAMETER, the system allocation mode can be set independent of the generation value and as a function of a specific disk.SPECIAL applications
The disk is reserved for a privileged application, e.g. VOLIN, FDDRL.
Special applications are always task-exclusive and system-exclusive allocations. The duration of an allocation is determined by the special application itself and cannot be influenced by the operator.
Dual recording by volume (DRV)
With the help of the DRV subsystem, not only public disks can be managed in duplicate but also private disks. Shared pubsets cannot be used for DRV. Each DMS write job is executed in duplicate and each read job is processed on the disk that is less heavily used at that time.
Requirements
In order for two disks to be operated as a single logical disk, the following conditions must be met:
the same device type
the same controller type
the same channel type
the same logical structure based on the same VOLIN parameters
the same VSN
the same time stamp
homogeneous entry for the DRV recording method
Operation and control
The entire functionality of DRV is implemented in the input/output system, in NDM and in the DRV subsystem and need not be considered either by DMS or by the application programs.
DRV operation is initiated, controlled, monitored and terminated exclusively by systems support.
The DRV product is described in detail in the “DRV” manual [17].