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

SET MDCACHE
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Set
Purpose
MDCache
Operands
FLUSH
INSert
vdev
vdev-vdev
ON
OFF
1286 z/VM: CP Commands and Utilities Reference
DIRectory
DRCT
Use SET MDCache to do the following:
v Set global minidisk caching on or off.
v Control minidisk caching at the real device or minidisk level.
v Change a user’s ability to insert data into the cache.
v Specify the maximum and minimum amounts of Real and/or Expanded Storage
that can be used by a minidisk cache. The actual size of the minidisk cache
varies and is determined dynamically by the paging and I/O load.
SYStem
RDEV
MDIsk
There is a hierarchy used to determine if a given virtual I/O will be cached.
These three keywords define which hierarchy level to which the command
pertains.
v The SYSTEM option is the highest level of control of the minidisk cache.
With the SYSTEM option, minidisk caching can be globally turned on
(enabled) or off (disabled) for the entire system via SET MDCACHE
SYSTEM ON and SET MDCACHE SYSTEM OFF. If minidisk caching is on at
the system level, it can be further controlled at the real device and minidisk
level.
v The RDEV option is the next highest level of control of the cache. If minidisk
caching is on for the system, the installation can change the cache eligibility
for a given real device, and hence, all minidisks that reside on that device via
SET MDCACHE RDEV action rdev (or SET MDCACHE RDEV action
rdev-rdev) where action is either DFLTON, DFLTOFF, OFF, or FLUSH.
v The MDISK option is the lowest level of control of the cache. If minidisk
caching is on for the system, the installation can change the cache eligibility
for an active minidisk via SET MDCACHE MDISK action USERID userid
vdev (or SET MDCACHE MDISK action USERID userid vdev-vdev). Note
that for a minidisk to be cached, the system must be enabled for caching, the
real device on which it resides must be set to DFLTON or DFLTOFF for
caching, and the minidisk itself must be enabled for caching.
Class G users can use the SET MDCACHE FLUSH vdev (or SET
MDCACHE FLUSH vdev-vdev) to purge the cache of data pertaining to
minidisks defined in their directory.
The duration of cache control at the minidisk level is not permanent when set
by the SET MDCACHE command. Permanent cache control at the minidisk
level is achieved by the use of the MDC and NOMDC options of the
MINIOPT directory control statement. For the SET MDCACHE command to
be successful for a minidisk, the minidisk must be active (that is, the minidisk
must be linked by at least one user who is logged on the system). If at a
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