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Monitor MONDCSS Segment

Last updated 02 December 2011


Computing the Size of the Monitor DCSS

The monitor DCSS is broken into two sections with 2 subsections in each. These are Sample (config, standard) and Event (config, standard).

AREA           Default Size in Pages  Change Size with this command
Sample Data     50% of seg - 4096     MONITOR START PARTITION n
Sample Config   4096                  MONITOR SAMPLE CONFIG SIZE n
Event  Data     50% of seg - 68       MONITOR START PARTITION n
Event  Config    68                   MONITOR EVENT CONFIG SIZE n
   Note: the MONITOR START PARTITION command sets size of EVENT partition
    with the left over being the Sample size.
   Note: as of z/VM 6.2.0 the default MONITOR SAMPLE CONFIG size is now
    4096 pages. If you define your own MONDCSS segment, the new default
    SAMPLE CONFIG size may be too large. If this is the case you will
    receive the following error message when you try to connect using
    the *MONITOR system service and the MONWRITE utility.
 
    HCPMOW6270E MONWRITE severed the IUCV connection, reason code 2C
    HCPMOW6267I MONITOR writer connection to *MONITOR ended
 
    If you receive this message you will have to increase the size of
    your MONDCSS segment or manually set the size of your SAMPLE
    CONFIG area using the MONITOR command.

So a monitor DCSS created by following commands -

       CP DEFSEG MONDCSS 9000-CFFF SC RSTD
       CP SAVESEG MONDCSS
 
would have a layout like the following:
 
208 M+---------------------+
     |                     |  S
     |                     |  A
     |     Data = rest     |  M
     |     4096 pages      |  P   8192 pages
     |.................... |  L
     | Config = 4096 pages |  E
176 M+---------------------+ ---
     |   (8124 pages)      |  E
     |   Data = rest       |  V
     |                     |  E  8192 pages
     |.....................|  N
     | Config = 68 pages   |  T
144 M+---------------------+
 
Note: This is the layout of the default MONDCSS segment shipped with z/VM
      starting with z/VM 6.2.0.

Use the Performance Manual section "Calculating the Space Needed for the Saved Segment" (Chapter 9) to compute size needed for the 4 areas. Assume the values you get are:

Sample Data     1886 pages
Sample Config    350 pages
Event  Data      256 pages
Event  Config     68 pages
 
You would need a 10 meg segment:
       CP DEFSEG MONDCSS 2200-2BFF SC RSTD
       CP SAVESEG MONDCSS
 
Set Config sizes:
       CP MONITOR SAMPLE CONFIG SIZE 350
       CP MONITOR EVENT  CONFIG SIZE  68
 
Start and set partition size:
       CP MONITOR START PARTITION 324
 
The layout would be:
 
44.0M+---------------------+
     |                     |
     |                     |
     |                     |  S
     |                     |  A
     | Data = 1886 pages   |  M
     |                     |  P   2236 pages
     |.................... |  L
     | Config = 350 pages  |  E
     |                     |
35.3M+---------------------+ ---
     | Data = 256 pages    |  E
     |                     |  V   324 pages
     |.....................|  E
     | Config = 68 pages   |  N
34.0M+---------------------+  T

To determine size of existing monitor DCSS, you will need to issue a few commands - QUERY NSS and QUERY MONITOR.

QUERY NSS NAME MONDCSS MAP results in -
 
FILE FILENAME FILETYPE MINSIZE  BEGPAG ENDPAG TYPE CL #USERS PARMREGS VMGROUP
0475 MONDCSS  CPDCSS     N/A    02200  02BFF   SC  R  00006   N/A       N/A
which tells us that the total size is 10 megabytes (2BFF minus 2200 plus 1 page). Then the output from QUERY MONITOR might look like this -
MONITOR EVENT ACTIVE    BLOCK    4     PARTITION     324
MONITOR DCSS NAME - MONDCSS
CONFIGURATION SIZE       68 LIMIT         1 MINUTES
CONFIGURATION AREA IS FREE
USERS CONNECTED TO *MONITOR - PERFSVM
MONITOR   DOMAIN ENABLED
PROCESSOR DOMAIN DISABLED
STORAGE   DOMAIN DISABLED
SCHEDULER DOMAIN DISABLED
SEEKS     DOMAIN DISABLED
USER      DOMAIN DISABLED
I/O       DOMAIN DISABLED
APPLDATA  DOMAIN DISABLED
MONITOR SAMPLE ACTIVE
               INTERVAL    1 MINUTES
               RATE     2.00 SECONDS
MONITOR DCSS NAME - MONDCSS
CONFIGURATION SIZE      350 LIMIT         1 MINUTES
CONFIGURATION AREA IS FREE
USERS CONNECTED TO *MONITOR - PERFSVM
MONITOR   DOMAIN ENABLED
SYSTEM    DOMAIN ENABLED
PROCESSOR DOMAIN ENABLED
STORAGE   DOMAIN ENABLED
USER      DOMAIN ENABLED
   ALL USERS ENABLED
I/O       DOMAIN ENABLED
   ALL DEVICES ENABLED
APPLDATA  DOMAIN ENABLED
   ALL USERS ENABLED
From this you can see that of the 2560 pages (10MB), 324 belong to Event. This leaves 2236 for Sample. Of the 324 for Event, 68 are for configuration. Of the 2236 for Sample, 350 are for configuration.

NOTE: If the size of the Sample Configuration Record area is too small, missing or incomplete monitor records can occur. This usually happens when there are a large number of devices available on your system. To increase the size of the Sample Configuration Record area use the MONITOR SAMPLE CONFIG command with the SIZE option.

If you are using IBM Performance Toolkit for z/VM (PERFKIT module) the missing and/or incomplete monitor records are detected when you start Performance Toolkit for z/VM and the message FCXPMN446E Incomplete monitor data: SAMPLE CONFIG size too small will be issued.


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