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

QUERY SCMBKS
QUERY SCMBKS
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Query
Authorization
Purpose
SCMBKs
Usage Notes
Responses
Privilege Class: B, E
Use QUERY SCMBKS to display the:
v Total number of subchannel measurement blocks (SCMBKs) that CP allocated,
and
v Number (and percentage) of SCMBKs that are not currently being used.
Format-1 measurement blocks: When format-1 measurement blocks are being
used, measurement blocks are allocated dynamically.
1. SCMBKs are used to accumulate data about a subchannel, such as rate and
utilization information. This subchannel measurement data, which CP Monitor
collects in various monitor records, can be useful for analyzing the I/O
performance characteristics of a real device.
Format-0 measurement blocks:
982 z/VM: CP Commands and Utilities Reference
1. During initialization, CP allocates 1 SCMBK for every subchannel on the
system and rounds the amount of storage up to the nearest page boundary.
Thus, you have enough SCMBK space for every real device on your system
plus some free SCMBK space. How much free SCMBK space you have will
vary, depending upon how many real devices you have on your system.
2. You should plan for additional SCMBK space if you intend to dynamically add
new real devices to your running system. At initialization, you can allocate more
free SCMBK space than CP would normally allocate using the SCMBK operand
of the STORAGE statement in the system configuration file. For more
information, see the z/VM: CP Planning and Administration book.
3. If you run out of free SCMBK space on a running system and you need to
measure additional real devices, you have two choices:
a. Re-IPL and specify more free SCMBK space using the SCMBK operand, or
b. Stop collecting subchannel measurement data for one or more devices.
When you use one of the following commands:
v DELETE DEVICE (page 223)
v DELETE IODEVICE (page 223)
v DELETE RDEVICE (page 228)
v SET SCMEASURE OFF (page 1377)
CP returns the SCMBK assigned to that device (or devices) to the pool of
available SCMBKs. It is then available to be used to collect subchannel
measurement data for another device.
To see information about the number of SCMBKs that CP allocated and information
about the free SCMBK space, enter the following QUERY SCMBKS command:
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