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

RETAIN XSTORAGE/XSTORE
Usage Notes
1174 z/VM: CP Commands and Utilities Reference
OFF
indicates that CP does not use XSTORE for minidisk cache. Main storage may
still be used for minidisk cache. The XSTORE portion of the minidisk cache is
set to 0 MB.
0M
minM
indicates the minimum size of the XSTORE portion of the minidisk cache in
megabytes — min can be from 0 to 16777216. If minM is specified, maxM must
also be specified. If minM is not specified, a value of 0 MB is assumed.
MAX
maxM
indicates the maximum size of the XSTORE portion of the minidisk cache in
megabytes — max can be from 0 to 16777216. If minM is specified, max must
be greater than or equal to min.
If MAX is specified for the maximum size of the XSTORE portion of the minidisk
cache, the upper limit of the XSTORE portion of the minidisk cache is set to the
size of the CP partition. If the value specified as max is 0, XSTORE is not used
for the minidisk cache.
When min equals max, the size of the XSTORE portion of the minidisk cache is
fixed. It does not vary dynamically.
1. If the amount specified is greater than the amount available, the amount
specified is rounded down to the amount available.
2. Issuing the RETAIN XSTORE command at initialization suspends virtual
machine execution until Expanded Storage initialization completes. To avoid
this, you can (a) wait until XSTORE initialization completes to enter RETAIN
XSTORE or (b) Enter RETAIN XSTORE from a disconnected virtual machine
that has been automatically logged on.
3. In the initial state, all the Expanded Storage is assigned to the CP partition, and
none is retained.
4. The RETAIN XSTORE command allows the class B operator to control the
amount of Expanded Storage that can be assigned to guest virtual machines. A
value of ALL inhibits the use of Expanded Storage by guest virtual machines
regardless of the user directory Expanded Storage statement and size value.
The user directory Expanded Storage size is the guest partition size
established, if the directory size is less than or equal to the maximum guest
partition size at logon. If the user directory size is greater than the maximum
guest partition, a guest partition equal to the maximum guest partition is
established.
5. If the RETAIN command is issued after Expanded Storage has been given to
the user, the response to the command may indicate that the amount retained is
less than the amount requested. In this case, pending retain is created.
To recover the Expanded Storage from a guest, use the following procedure:
a. The guest operator issues a guest operating system command to quiesce
the use of Expanded Storage in the guest; for example, if the quest is MVS,
the MVS operator issues the MVS VARY XSTORE OFFLINE command.
b. The guest operator issues CP DETACH XSTORE.
c. CP now acquires the Expanded Storage.
d. The guest operator or the CP operator issues the CP ATTACH XSTORE
command. (Note that ATTACH is a privilege class B command.)
e. The guest operator issues the VARY XSTORE ONLINE command.