Use of SM pubsets

Whereas the formatting attributes of a volume set, which are defined at initialization, remain unchanged for as long as it exists, the availability and performance attributes can be changed in the ongoing operation. Only the performance attributes are dealt with below.

SM pubsets from the point of view of the user

So called storage services can be requested for a file using /CREATE-FILE or /MODIFY-FILE-ATTRIBUTES (STORAGE-CLASS operand) or the FILE macro (STOCLAS operand), i.e., the file attributes which are relevant for the storage location:

Operand	Meaning
STORAGE-CLASS ́= *STD	Assigns the default storage class from the user catalog of the SM pubset.
STORAGE-CLASS = <name>	Assigns a specific storage class.
STORAGE-CLASS = *NONE	There is no explicit assignment of a storage class. The user defines the performance attributes (*STD / *HIGH / *VERY-HIGH / *USER-MAX).

The user can obtain information on the names and attributes of the available storage classes (i.e. access must be permitted when GUARDS protection is set) with /SHOW-STORAGE-CLASS.

The user can get information on the storage services of the existing volume sets with /SHOW-PUBSET-FILE-SERVICES and thus check whether there is a volume set with the desired attributes for his/her file.

The storage services can also be requested by means of direct attributing.

SM pubsets from the point of view of systems support

In order for the user's performance requirements for the volume sets of an SM pubset to become effective, corresponding authorizations and storage space quotas must be entered in the user catalog (/ADD-USER, /MODIFY-USER-ATTRIBUTES or /MODIFY-USER-PUBSET-ATTRIBUTES):

Operand	Meaning
DEF-STORAGE-CLASS = <name>	Default storage class for the user specification STORAGE- CLASS=*STD
DMS-TUNING-RESOURCES	For an explicit request via direct operand or implicitly via a storage class:
= *NONE	caching not permitted
= *CONCURRENT-USE	for PERFORMANCE=*HIGH
= *EXCLUSIVE-USE	for PERFORMANCE=*VERY-HIGH
PERM-/TEMP-/WORK-SPACE-LIMIT    = *PARAMETERS(...)	Defining the users' storage space quotas (in each case for permanent, temporary, and work files):
HIGH-PERF-SPACE= ...	for high-performance storage space
VERY-HIGH-PERF-SPACE= ...	for very high-performance storage space

Systems support uses /CREATE- or /MODIFY-STORAGE-CLASS to create or modify storage classes.

When the user assigns a storage class to a file, this file implicitly receives all the performance attributes set in the storage class.

Operand	Meaning
PERFORMANCE	Defines the caching behavior (main memory):
= *STD	No cache usage
= *HIGH	Caching with preemption on the basis of LRU
= *VERY-HIGH	caching without preemption
USAGE	Increased performance requirements apply:
= *READ-WRITE	to read and write operations
= *READ	to read operations only
= *WRITE	to write operations only
DISK-WRITE	Specifies when data consistency is restored:
= *IMMEDIATE	Data consistency after every write operation (prerequisite: non-volatile cache medium)
= *BY-CLOSE	Data consistency after CLOSE processing
= *STD	*IMMEDIATE applies for permanent files, *BY-CLOSE applies for temporary files
VOLUME-SET-LIST	Assigns a volume set list
= <name>	Assigns a specific volume set list
= *NONE	No volume set list is assigned

To meet higher performance requirements (*HIGH / *VERY-HIGH), systems support must assign main memory as the cache medium (/MODIFY-PUBSET-CACHE-ATTRIBUTES).

When a volume set list is specified for each storage class, computer center-specific strategies for controlling input/output distribution can be implemented. If a user assigns a storage class with an associated volume set list to a file, the file is created, if possible, on a volume set contained in the list. A volume set list is created using /CREATE-VOLUME-SET-LIST.

The performance characteristics of a volume set are defined with /MODIFY-PUBSET-DEFINITION-FILE:

Operand	Meaning
PERFORMANCE	Defines the caching behavior (main memory):
= *STD	No cache usage
= *HIGH	Caching with preemption on the basis of LRU
= *VERY-HIGH	caching without preemption
= list-poss(3) ...	List of values permits a performance range
WRITE-CONSISTENCY	Specifies when data consistency is restored:
= *IMMEDIATE	Data consistency after every write operation (prerequisite: non-volatile cache medium)
= *BY-CLOSE	Data consistency after CLOSE processing

Volume set selection will not function properly unless the performance profile is described adequately. The performance profile is not determined automatically on the basis of the physical configuration. It is the job of systems support to describe the real conditions accurately (taking into account a volatile or non-volatile cache medium when assigning WRITE-CONSISTENCY).