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

SET MDCACHE
the virtual machine issuing the command. For the class B command, if DRCT or
DIRectory is not specified, the userid specified must be logged on.
vdev
vdev-vdev
identifies the virtual device number or the range of virtual device numbers for
which cache settings are to be changed. For the class B command, the virtual
device numbers specified correspond to the userid’s current configuration if the
DIRECTORY or DRCT option is not specified and to the userid’s directory entry
if the DIRECTORY or DRCT option is specified.
DIRectory
DRCT
indicates that the virtual device numbers correspond to the userid’s directory
entry. For the class B command, if DRCT or DIRectory is not specified, the
userid specified must be logged on.
RECORDMDc
indicates that the minidisk’s data should be cached using 4K record caching
instead of normal full track caching. Only non-FBA 4K CMS formatted I/O via
Diagnose X'18', X'A4', X'250', and *BLOCKIO CP System Service is cached. All
other I/O results in I/O direct to the minidisk. This option is only valid for SET
MDCACHE MDISK ON.
CAUTION:
Use of this option is a last resort for very special and unusual
circumstances. It should only be used as the result of consultation with
IBM support personnel who have concluded that no other performance
problem exists. Using this option for any other reason may mask a
performance problem which when corrected allows normal full track
minidisk cache to perform better than with the RECORDMDC option.
INSert
changes a user’s ability to insert information into the cache.
v The ON option allows a user to insert data into the cache.
v The OFF option prevents a user from inserting data into the cache. The user
will continue to use data that is already in the cache, but cannot insert data.
This option is useful when doing a scan of multiple files to avoid corrupting
the cache with data that will only be referenced once.
STorage
XSTore
used to control the size of the real storage portion (STORAGE) or the expanded
storage portion (XSTORE) of the minidisk cache or enable/disable caching to
real or expanded storage.
ON
1288 z/VM: CP Commands and Utilities Reference
indicates that CP uses the amount of minidisk cache that best balances I/O and
paging performance. This is the default. For expanded storage, the minidisk
cache size can range from 0 to the size of the CP partition. For real storage,
the minidisk cache can range from 0 to the size of real storage, although the
actual maximum is really limited to the size of the DPA.
ALL
indicates that CP uses the CP partition of Expanded Storage exclusively for
minidisk cache. CP does no paging to Expanded Storage. This option is only
valid for SET MDCACHE XSTORE.