Use this command to update a device class that you defined to use a z/OS® media server to access files on magnetic disk storage as sequential-access volumes (like tape). The device class that targets storage for the z/OS media server requires a library definition of type ZOSMEDIA.
A volume in this device class is a Virtual Storage Access Method (VSAM) linear data set that is accessed by the z/OS media server. SCRATCH volumes can be used with a device class and the z/OS media server dynamically allocates the VSAM LDS. It is not necessary to define volumes for the server to use the device class. If you define volumes, set the high-level qualifier (HLQ) so that SMS recognizes the allocation request by the z/OS media server. If you are using defined volumes, the format volume function is not supported for the server when you use this device class. The z/OS media server z/OS media server uses a FormatWrite feature of DFSMS Media Manager when filling FILE volumes.
You can define volumes for the FILE device class by using the DEFINE VOLUME command. However, the z/OS media server does not allocate space for a defined volume until the volume is opened for its first use.
Privilege class
To issue this command, you must have system privilege or unrestricted storage privilege.
Syntax
>>-UPDate DEVclass--device_class_name---------------------------> >--+----------------------+--+-----------------------+----------> '-MAXCAPacity--=--size-' '-PRIMARYalloc--=--size-' >--+-------------------------+----------------------------------> '-SECONDARYalloc--=--size-' >--+-------------------------------+----------------------------> '-PREFIX--=--file_volume_prefix-' >--+-----------------------+----------------------------------->< '-MOUNTLimit--=--number-'
Parameters
- device_class_name (Required)
- Specifies the name of the device class to be defined. The maximum length of the device class name is 30 characters.
- MAXCAPacity
- Specifies the maximum size of file volumes that are defined to
a storage pool in this device class. This parameter is optional.
Specify this value as an integer followed by K (KB), M (MB), G (GB), or T (TB). The minimum size is 1 MB (MAXCAPACITY=1M). The maximum size is 16384 GB (MAXCAPACITY=16384G).
- PRIMARYalloc
- Specifies the initial amount of space that is dynamically allocated
when a new volume is opened. Enough space must be available to satisfy
the primary allocation amount. Storage Management Subsystem (SMS)
policy determines whether multiple physical volumes can be used to
satisfy the primary allocation request.
This parameter is optional. Specify this value as an integer followed by K (KB), M (MB), G (GB), or T (TB). The minimum size is 100 KB (PRIMARYALLOC=100K). The maximum size is 16384 GB (MAXCAPACITY=16384G). All values are rounded to the next higher multiple of 256 KB.
To avoid wasted space, the dynamic allocation operation uses the smaller of the values that are specified in the two parameters, PRIMARYALLOC and MAXCAPACITY.
SMS automatic class selection (ACS) routines can affect whether the PRIMARYALLOC and SECONDARYALLOC parameter values are used.
- SECONDARYalloc
- Specifies the amount of space by which a file volume is extended
when space that is already allocated to the file volume is used up.
The data set for a file volume is extended up to the size set by the MAXCAPACITY parameter,
then the volume is marked full.
Because secondary allocation of a linear data set cannot span a physical volume, consider the size of the physical volume when selecting a secondary allocation size. For example, physical volumes for a 3390 Model 3 are approximately 2.8 GB. To ensure that each extend request occupies nearly an entire physical volume but not more, use a secondary allocation size that is just less than 2.8 GB. A secondary allocation amount of 2600 MB allots enough space for the VSAM volume data set (VVDS), the volume label, and the volume table of contents (VTOC).
This parameter is optional. Specify this value as an integer followed by K (KB), M (MB), G (GB), or T (TB). The minimum value is 0 KB (SECONDARYALLOC=0K). The maximum value is 16384 GB. Except for 0, all values are rounded to the next higher multiple of 256 KB.
If you specify 0 (SECONDARYALLOC=0), the file volume cannot be extended beyond the primary allocation amount.
SMS automatic class selection (ACS) routines can affect whether the PRIMARYALLOC and SECONDARYALLOC parameter values are used.
If you specify a value for the SECONDARYALLOCATION parameter that is not 0, or if you allow the value to default to 2600M, the SMS DATACLAS associated with the PREFIX identifier (for example, High Level Qualifier) must have the Extended Addressability (EA) attribute specified. Without the EA attribute, the SMS DATACLAS limits the allocation of the VSAM LDS FILE volume to the primary extent. (See the description of the PRIMARYALLOCATION parameter). With the data set limited to primary allocation size, the data set cannot be extended by the z/OS media server, and the volume is marked FULL before the maximum capacity is reached.
Restriction: Ensure that the values that you specify for the PRIMARYALLOC and SECONDARYALLOC parameters are within practical limits for the storage device. The server cannot check whether the values exceed practical device limits, and does not check whether the two values together exceed the current MAXCAPACITY setting.Tip: To fill volumes when you specify a large value for the MAXCAPACITY parameter, specify large values for the PRIMARYALLOC and SECONDARYALLOC parameters. Use larger MVS™ volume sizes to reduce the chance of extend failure. - PREFIX
- Specifies the high-level qualifier of the data set name that is
used to allocate scratch volume data sets. For all scratch file volumes
created in this device class, the server uses this prefix to create
the data set name. This parameter is optional. The maximum length
of the prefix, including periods, is 32 characters. Values specified for this parameter must meet the following conditions:
- The value is to be made up of qualifiers, which can be a maximum
of eight characters including periods. For example, the following
value is acceptable:
AB.CD2.E - The qualifiers must be separated by a single period.
- The first letter of each qualifier must be alphabetic or national (@,#,$), followed by alphabetic, national, hyphen, or numeric characters.
An example of a file volume data set name using the default prefix is ADSM.B0000021.BFS.
If you have a data set naming convention, use a prefix that conforms to your naming conventions. For example, the following value is acceptable: TSM.SERVER2.VSAMFILE.
If you are running multiple server instances for either Tivoli® Storage Manager or Tivoli Storage Manager for z/OS Media you must use a unique value for the PREFIX parameter for each device class that you update.
- The value is to be made up of qualifiers, which can be a maximum
of eight characters including periods. For example, the following
value is acceptable:
- MOUNTLimit
- Specifies the maximum number of FILE volumes
that can be open concurrently for this device class. This parameter
is optional. For 3995 devices emulating 3390 devices, the value must
not be set higher than the numbers of concurrent input and output
streams possible on the media storing the volumes.
The value that you specify in this parameter is important if there is a significant penalty switching from one volume to another. For example, switching can take place when using IBM® 3995 devices to emulate 3390 devices. The value that you specify must be no higher than the number of physical drives available on the device.
If you plan to use the simultaneous-write function, ensure that sufficient drives are available for the write operation. If the number of drives needed for a simultaneous-write operation is greater than the value of the MOUNTLIMIT parameter for a device class, the transaction fails.