Data management

Management of volumes and access paths

The device management facility consists essentially of the following components:

• Resource allocation
  This function controls and monitors the logical statuses (occupied/available) of the resources (devices, volumes) requested by the user.

• Resource reservation
  This function processes requests for resources. These requests are formulated by the user with the aid of /SECURE-RESOURCE-ALLOCATION.

• Reconfiguration
  This function permits the operator to add or remove hardware units and their virtual connections on the command level.

• Volume monitoring
  This function monitors the accessibility of volumes, particularly during mounting procedures.

In the case of resource allocation the following points should be noted with reference to system overhead:

Each time a volume is occupied, information to this effect is stored in its standard volume label (SVL). In the case of private volumes, system overhead varies, depending on the type of allocation (task-exclusive/task-shareable) and the time the allocation is made (ASSIGN-TIME=*USER/*OPERATOR).

• When the time the allocation is made is determined by the user and the allocation is task-exclusive using the command

  /SET-DISK-PARAMETER VOLUME=vsn,ASSIGN-TIME=*USER, USER-ALLOCATION=*EXCLUSIVE

  the SVL on the volume is updated at the beginning and end of each file operation involving catalog access (/COPY-FILE, /DELETE-FILE, /CREATE-FILE, /MODIFY-FILE-ATTRIBUTES, OPEN, CLOSE).

• When the time the allocation is made is determined by the user and the allocation is task-shareable using the command

  /SET-DISK-PARAMETER VOLUME=vsn,ASSIGN-TIME=*USER, USER-ALLOCATION=*SHARE

  the SVL is read when the first user attempts access, and written back when the volume is released by the last user. In the meantime, the SVL on the volume is not updated, but internal table management activities take place whenever there is a file operation involving catalog access.

• When the time the allocation is made is determined by the system (activation interrupt) SVL updating is performed once for each session, regardless of the type of allocation.

Recommendations

• The system should determine the time of allocation.
  This is set by means of folloiing command:

  /SET-DISK-PARAMETER VOLUME=vsn,ASSIGN-TIME= *OPERATOR,USER-ALLOCATION=*EXCLUSIVE/*SHARE

  Release of the volume (special case) can be performed by means of:

  /SET-DISK-PARAMETER VOLUME=vsn,ASSIGN-TIME=*USER