z/VM: CP Commands and Utilities Reference - z/VM - IBM

SET MDCACHE
Responses
5. If SET MDCACHE XSTORE maxM or SET MDCACHE STORAGE maxM is
issued when max is greater than the current size of the minidisk cache in
expanded storage or main storage, a gradual reduction in the use of Expanded
Storage or main storage for CP paging occurs until the minidisk cache attains
the new size. This does not cause a rapid migration of paging data to auxiliary
storage. Similarly, when max is less than the current size of the minidisk
cache, a gradual reduction in the use of minidisk cache occurs until the
minidisk cache attains the new size.
6. SET MDCACHE XSTORE performs the same function as RETAIN XSTORE
MDC. Either command can be used to adjust the XSTORE portion of the
minidisk cache. SET MDCACHE STORAGE is the only command that can be
used to adjust the main storage portion of the minidisk cache.
7. Using the DIRectory or DRCT options is highly recommended as the user’s
current virtual configuration could vary between the time a user’s virtual device
is queried and the time the SET MDCACHE command is issued. The SET
MDCACHE command could end up being issued for the wrong virtual device.
8. It is recommended that if minidisk caching is used, that main storage is not set
to off. Even it is set to off, up to 1 Megabyte of main storage may be used for
minidisk caching.
9. The RECORDMDC option of the SET MDCACHE MDISK ON command
should only be used when directed to do so by IBM support personnel.
RECORDMDC is for use only when DASD cache as well as main storage and
expanded storage minidisk cache are all being overwhelmed by excessive
unreferenced records being read by the full track cache support.
10. Use the SET MDCACHE INSERT command to termporarily disable minidisk
cache operation for a minidisk (for example: during backup for the minidisk).
Do not use SET MDCACHE MDISK as this causes unnecessary overhead and
may cause a change in the caching mode for this minidisk.
Response 1:
1290 z/VM: CP Commands and Utilities Reference
The following response is issued when you specify SET MDCache SYStem ON, or
SET MDCache STorage/XSTore.
Minidisk cache ON for system
Storage MDC min=nnnM max=nnnM, usage=ppp%, bias=b.bb
Xstore MDC min=nnnM [(nnnM pending)] max=nnnM
[(nnnM pending)], usage=ppp%, bias=b.bb
min=nnnM
indicates the current minimum value for the size of minidisk cache in
megabytes. For expanded storage, this may change as the CP partition size
changes.
(nnnM pending)
identifies the amount by which the specified value exceeds the current CP
partition size. This means that the minimum/maximum amount of Expanded
Storage for MDC could not be fully satisfied. When the missing amount
becomes available to CP, it is added to the minimum/maximum MDC size value.
This data is shown only if the pending amount is not equal to zero.
max=nnnM
indicates the current maximum value for the size of minidisk cache in
megabytes. For expanded storage, this may change as the CP partition size
changes.