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Administrator's Guide


Defining FILE Device Classes

The FILE device type is used for special device classes whose storage volumes are not physical units, such as tape cartridges, but simulated storage volumes. Data is written sequentially into standard files.

Note:
Because each volume is actually a file, a volume name is a fully qualified data set name.

Other parameters specify how to manage data storage operations for the new device class:

Device Type

You define the FILE device class by specifying the DEVTYPE=FILE parameter with the DEFINE DEVCLASS command.

Mount Limit

The mount limit value for FILE device classes is used to restrict the number of volumes (that is, files) that can be concurrently opened for access by data storage and retrieval operations. Any attempts to access more volumes than indicated by the mount limit causes the requester to wait.

See Mount Limit for a discussion of the considerations necessary in determining an appropriate mount limit value for the new device class.

Maximum Capacity

You can specify a maximum capacity value that restricts the size of volumes (that is, files) associated with a FILE device class. If you are explicitly allocating FILE volume data sets, be sure the allocated capacity matches the maximum capacity. File volumes are allocated in 16KB blocks. Thus, if the maximum capacity is 50MB, you should allocate 3200 blocks. A combination of primary and secondary extents may be specified to achieve the allocation. When the server detects that a volume has reached a size equal to the maximum capacity, it treats the volume as full and tries to store any new data on a different volume.

Note:
File volumes of 256MB or smaller will be allocated with a single primary extent. File volumes larger than 256MB will be allocated with a 256MB primary extent and secondary extents of 1/15 of the remaining required space.

The default MAXCAPACITY value for a FILE device class is 1MB. Once the device class is defined, the maximum capacity value cannot be changed.

Prefix

This parameter is the MVS high-level qualifier used to allocate scratch volume data sets.


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