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

Usage Notes
SET MDCACHE
OFF
indicates that CP does not use any of the identified storage for minidisk
caching. The minidisk cache size is set to 0 for the specified storage type.
BIAS number
designates a number (value) that the MDC arbiter will use to adjust the target
size for the indicated storage. The number must be within the range .01 to
100.00. For whole numbers, the decimal point is optional. The arbiter will
multiply its selected target size by number and use the product (subject to the
specialized min and max ranges) as the new target size. Therefore, if the
number is greater than one, the effective target size will be larger than the one
chosen by the arbiter and if the number is smaller, the target will be
correspondingly smaller.
0M
minM
indicates the minimum size of the minidisk cache in megabytes if 0M or minM.
If min is greater than the amount of expanded or main storage on the system,
the value is decreased to the amount of expanded or main storage on the
system. If minM is specified, maxM must also be specified. If minM is not
specified, the current minimum does not change unless it is now larger than the
maximum in which case it is set to equal the maximum.
MAX
maxM
indicates the maximum storage size in megabytes for the indicated storage. If
max is greater than the amount of expanded or main storage on the system,
the value is decreased to the amount of expanded or main storage on the
system. If minM is specified, max must be greater than or equal to min. If MAX
is specified for the maximum expanded storage size, the upper limit of the
minidisk cache is set to the size of the CP partition. If MAX is specified for the
maximum real storage size, the upper limit of the real storage portion of the
minidisk cache is set to the size of online real storage.
If the value specified as max is 0, the minidisk caching is turned off for that type
of storage. Setting the maximum value to 0 is likely to degrade performance.
The smallest recommended value is 2M.
When min equals max, the size of the minidisk cache is fixed for that type of
storage. It does not vary dynamically.
1. In z/Architecture mode, MDC uses host real storage above the 2G line.
2. If the amount specified via SET MDCACHE STORAGE or SET MDCACHE
XSTORE is greater than the amount available, the amount specified is
rounded down to the amount available.
3. Issuing both SET MDCACHE XSTOR OFF and SET MDCACHE STOR OFF or
issuing SET MDCACHE SYSTEM OFF prevents caching from occurring on the
system. However, issuing SET MDCACHE SYSTEM OFF immediately purges
all cache data, disables caching on the system, cleans up all internal minidisk
cache structures, and releases all storage used by caching. Issuing SET
MDCACHE XSTORE OFF and SET MDCACHE STOR OFF causes a gradual
reduction in cache data and does not clean up internal structures or storage.
Furthermore, caching is still considered enabled for the system.
4. When SET MDCACHE XSTORE or SET MDCACHE STORAGE is issued with
any option other than OFF, minidisk caching is enabled.
Chapter 2. CP Commands 1289