The performance-related file attributes PERFORMANCE, USAGE and DISK-WRITE are used to control cache utilization in the Hiperfile concept:
PERFORMANCE
specifies the required performance for file access input/output behaviorUSAGE
describes whether the performance is only required for read or write or for both access typesDISK-WRITE
defines the time during cache-assisted file processing when the data must be consistent for write operations
PFA for SF pubsets
With SF pubsets, the performance-oriented file attributes control cache use: a file for which enhanced performance was requested is automatically cached during processing. When this is done, the values specified for USAGE and DISK-WRITE and the cache type (VOLATILITY) assigned to the pubset determine whether read and/or write caching is performed.
If the file attributes PERFORMANCE=*HIGH, USAGE=*READ-WRITE and DISK-WRITE=*IMMEDIATE are selected for a file written to an SF pubset with a non-write-secure cache (e.g. main memory cache) then cache buffering is read only since the preconditions for the failproof caching of write I/Os are not fulfilled. The user is responsible for ensuring that the file attributes he specifies comply with the cache properties.
The command SHOW-MASTER-CATALOG-ENTRY INF=*USER displays in the CACHE-MEDIUM output line whether non-volatile cache medium is assigned to the pubset. This is true if NONVOLATILE is output; only then are the file attributes USAGE=*WRITE and DISK-WRITE=*IMMEDIATE are then effective.
Systems support can use the SHOW-PUBSET-CACHE-ATTRIBUTES command to display the complete cache configuration of SF pubsets.
Systems support should configure the cache area of a pubset in such a way that users do not have to assign attributes to their files themselves in order to achieve enhanced performance: MODIFY-PUBSET-CACHE-ATTRIBUTES command, CACHED-FILES=*BY-SYSTEM operand.
In these cases, the default values for the file attributes ensure that write caching is performed only to failproof media. Read caching is always performed.
PFA for SM pubsets
For SM pubsets, the performance-oriented file attributes are used for selecting the most suitable volume set for file storage during volume set selection: when a new file is created, its performance attribute is used to automatically store it on the volume set whose performance profile most closely matches the file requirements.
The performance profile of a volume set results from its performance spectrum and the restrictions imposed by its write security requirements when using enhanced performance values. It can be defined with the PERFORMANCE-ATTR operand of the MODIFY-PUBSET-DEFINITION-FILE command and retrieved with the command SHOW-PUBSET-DEFINITION-FILE.
Systems support is responsible for ensuring that the performance profile of a volume set is supported by adequate provision of hardware or cache configurations with the MODIFY-PUBSET-CACHE-ATTRIBUTES (EDIT-PUBSET-CACHE-ATTRIBUTES) command. For details and recommendations regarding the performance profile for SM pubsets, see section "Defining the performance profile".
Volume set configuration | Recommended performance (Performance spectrum) | Recommended performance with enhanced performance |
Volume set made up of volumes with no special performance properties and with no cache assigned | STD | irrelevant |
Volume set which is assigned main memory as the cache medium | STD, HIGH | not satisfied (BY-CLOSE) |
Volume set whose volumes are connected to a cache controller | STD, HIGH | satisfied (IMMEDIATE) |
Table 17: Recommendations for performance profiles
Systems support can display the set cache configurations of the volume sets in an SM pubset with SHOW-PUBSET-CACHE-ATTRIBUTES ...,VOLUME-SET=*ALL/<cat-id 1..4>.