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/Awhich 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 ENABLEDFrom 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.
Back to the Performance Tips Page