Memory management is performed by the system and offers optimal support for calls using catalog access:
a high degree of user convenience by means of considerable simplification of the definitions for creating, extending and deleting files
a lower number of management I/Os compared with private volumes (management of F5 labels in main memory, support from the software product SCA, see "Accelerating catalog accesses with SCA").
The location of a file can be specified explicitly for all pubsets by systems administration. and for selected pubsets by the user as well, where the authorization for physical allocation is entered in the pubset-specific user catalog (/MODIFY-USER-ATTRIBUTES, PHYSICAL-ALLOCATION operand).
Pubsets are the strategic platform for further developments in the disk area. Private volumes do not offer full functional support of new functions, e.g. in the HIPERFILE concept.
Migration from private volumes to pubsets is thus recommended.
SF pubsets
As far as memory management is concerned, the same applies as for public volumes. In addition to an increase in availability, the following advantages can be seen as far as performance is concerned (particularly important for interactive mode):
Splitting the file catalog TSOSCAT over separate pubsets improves catalog performance if the catalog functions are used intensively.
It is possible for systems support to control input/output distribution by means of the user catalog entries. Users with files subject to particularly frequent access can be transferred to separate pubsets.
SM pubsets
SM pubsets consist of a number of volume sets that may have different formatting, availability and performance attributes specified by systems support.
In comparison to SF pubsets, which consist of a single volume set, SM pubsets offer better control of input/output distribution to systems support and greater convenience to users:
By specifying direct attributes or a storage class when creating a file, a user can specify where the file is to be stored on an SM pubset.
Systems administration assigns a volume set list to each storage class and defines the desired performance requirements for each volume set.
You will find detailed information on SMS (System Managed Storage) and SM pubsets in the “SMS” manual [33 (Related publications)].
Shared pubsets
Two or more write-authorized servers (or guest systems under VM2000) can access shareable pubsets simultaneously (except in the case of the home and paging pubsets). The systems are interconnected via a BCAM link and work according to the master/slave principle. All catalog operations (RDCAT, WRCAT, etc.) are always performed by the master system. It is thus only practical to use SCA in the master.
Taking into account the following points, the performance behavior is virtually the same as for “normal” public volumes:
the system from which most accesses are performed is set as the master (to minimize cross-system actions)
to keep the overhead for cross-system actions to an acceptable level, no more than two OPEN/CLOSE operations per second should be carried out on the slave systems for each RPF (Relative Performance Factor).