SF pubsets are built by combining volumes whose attributes should match. These should have identical features since differences between the volumes are not taken into account when the system allocates storage space to files. Caches are assigned at pubset level, not at volume level. (Homogeneous) pubsets are thus containers for files that can be characterized by a specific attribute profile (K or NK2 pubset, DRV pubset, etc.).
Different attribute profiles must be implemented by a set of different SF pubsets. It is the users' task, within the limits of their authorizations, to select those pubsets as storage locations for their files that are best suited to their requirements. To be able to select the appropriate pubsets, users require information about the computer center's configuration. The following interfaces are provided to obtain information about installed pubsets and their attributes:
The information blocks SUMMARY and PHYSICAL-CONFIGURATION output by the SHOW-PUBSET-CONFIGURATION command supply information about the pubset type (SF or SM), the volumes of the pubset, their device type as well as any allocation constraints that may apply to the volumes (unrestricted allocation, only physical allocation permitted, allocation prohibited).
The SHOW-MASTER-CATALOG-ENTRY command and the STAM macro indicate the global features of an SF pubset with respect to cache assignment, availability, structure, allocation unit, etc.
Once the user has selected a suitable pubset for a file, the selection must be communicated to the system. This is done via the path name of the file which includes the catalog ID of the pubset on which the file is to reside. The catalog ID need not be specified explicitly, i.e. file names without a catalog ID specification are permissible also. In this case, the system determines the full path name automatically on the basis of the user-specific default catalog ID.
Determining the file format
In contrast to SM pubsets, no preformat is required. The file format as reflected in the attributes BLOCK-CONTROL-INFO (or BLKCTRL) and BUFFER-LENGTH (or BLKSIZE) is determined analogously. The attributes are not determined until the file is opened (OPEN macro, OPEN mode OUTPUT or OUTIN). The following factors are decisive for the file format:
the attribute values for FCBTYPE, BLKCTRL and BLKSIZE
the format of the actual file location
Usually, the specified attribute values are taken to determine the file format, or the following defaults are assumed:
Disk format | Default for BLKSIZE |
|---|---|
K / NK2 | (STD,1) |
NK4 | (STD,2) |
Disk format | FCBTYPE | Default for BLKCTRL |
|---|---|---|
K | any | PAMKEY |
NK2 / NK4 | SAM | DATA |
NK2 / NK4 | PAM | NO |
NK2 | ISAM | DATA2K |
NK4 | ISAM | DATA4K |
The following modifications are applied during OPEN processing if any specifications are incompatible with the access method:
FCBTYPE | Old BLKCTRL value | New BLKCTRL value |
|---|---|---|
SAM | DATA2K / DATA4K / NO | DATA |
PAM | DATA2K / DATA4K | NO |
ISAM | DATA / NO |
|
Any specification for BLKCTRL and BLKSIZE that is incompatible with the disk format will be rejected, e.g.:
BLKSIZE=(STD,1) and BLKCTRL=DATA4K
BLKSIZE=(STD,1) for a file residing on an NK4 disk
BLKCTRL=DATA4K, BLKSIZE not specified, FCBTYPE=ISAM for a file residing on a a K or NK2 disk.