MONITOR DATASPACE command

Summary

Privileges

System administrator

Function

Enables the system administrator to display the use of dataspaces and hiperspaces when tracking the use of the CCATEMP and CCASERV In Storage feature.

Syntax

MONITOR DATASPACE

Example 1

The DATASPACE option of the MONITOR command displays dataspace and hiperspace information as shown in the following example. Hiperspace is an area of virtual storage requested from the hardware's expanded storage. Access to hiperspace saves you from paging out to disk.

NAME STORAGE TYPE 4K PAGES PAGE HWM EXTRA DATASPACES -------- ------------------- ---------- ---------- ---------------- CCASERVR 64-BIT MEMORY 1465 1440 CCATEMP 64-BIT MEMORY 15100 0 CCAAPSY 64-BIT MEMORY 1000 0 NAME READS WRITES PAGES READ PAGES WRITN SLOWRD SLOWWR PAGEF -------- ------ ------- ----------- ------------ ------- ------- ------ CCASERVR 13 20 1261 1940 0 0 0 CCATEMP 0 0 0 0 0 0 0 CCAAPSY 0 0 0 0 0 0 0

The explanation of the headings in the previous example are:

Heading	Meaning
NAME	Dataspace or hiperspace name
STORAGE TYPE	Type may be one of the following: Dataspace Hiperspace scroll Hiperspace cache 64-bit memory
4K PAGES	Number of 4K pages in a dataspace or a hiperspace
PAGE HWM	The highest 4K-page number used in a dataspace or a hiperspace
EXTRA DATASPACES	List of additional dataspace names allocated to accommodate the total number of pages. Each dataspace or hiperspace may not have more than 524,288 4K pages. Additional dataspace or hiperspace names are constructed as CCA00001, CCA00002
READS	Number of read operations against a dataspace or a hiperspace
WRITES	Number of write operations against a dataspace or a hiperspace
PAGES READ	Number of 4K pages read from a dataspace or a hiperspace
PAGES WRITN	Number of 4K pages written to a dataspace or a hiperspace
SLOWRD	Number of 4K pages read from a dataspace or a hiperspace without the Move Page instruction.
SLOWWR	Number of 4K pages written to a dataspace or a hiperspace without the Move Page instruction.
PAGEF	Number of page faults when reading 4K page from a cache hiperspace. The statistics indicates how many times Model 204 had to do a disk read due to a 4K page fault in a cache hiperspace

See DSPOPT: Dataspace and hiperspace options for an explanation of the terms DATASPACE TYPE, SLOWRD, and SLOWWR.

Usage

Among things monitored are page usage high-water marks, number of calls to the dataspace data movement routines, the quantity of data moved to and from the dataspaces, and page-fault statistics for dataspace data movement.

Since IBM support for access to real storage above two gigabytes is limited to 2-gigabyte chunks of storage, multiple 2-gigabyte dataspaces are chained together and logically mapped as either CCATEMP or CCASERVR.

Under the 4K PAGES heading, each X'00080000' number of 4K blocks is a 2-gigabyte chunk. There are two logical dataspaces, CCATEMP and CCASERVR. However, since IBM requires that every dataspace be named, the additional (if required) physical, 2-gigabyte chunks have generated sequential names beginning with CCA00001.

Considering the SLOWRD and SLOWWR statistics

The SLOWRD and SLOWWR statistic occur when Model 204 uses the Assembly Language Move Character Long (MVCL) facility, instead of the Assembly Language Move Page (MVPG) facility to move a 4-K page to or from a CCASERVR or CCAAPSY dataspace. This happens when the page that you referenced in the dataspace is not in memory. A page fault occurs and MVPG fails with a nonzero return code. When that happens, Model 204 switches to MVCL and moves the page. MVCL waits for the page fault to resolve, whereas MVPG does not. When this switching takes place you will see SLOWRD and SLOWWR statistics increase, although usually they are not significant.

In the MONITOR DATASPACE output check whether less than 20 percent of PAGES WRITN were SLOWWRs. If the percentage gets higher, it indicates that memory for dataspaces or hiperspaces is constrained and that the pages referenced when you do a server swap or an APSY load are not in memory.

The percentage of SLOWRDs and SLOWWRs generally does not represent a problem unless the percentages compared to PAGES READ or PAGES WRITN exceed 20-30 percent. Then, the only action you can take to reduce the percentages is by adding more central or expanded storage or by reducing the size of the CCASERVR or CCAAPSY dataspaces.

Example 2

Output from the operating system

There are five physical dataspaces in the following example. When a TSO user issues the following command, where DVUSER2 is the job name of the Online using the dataspaces, the following output is displayed:

/D J,DVUSER2 IEE115I 11.27.40 2001.155 ACTIVITY 900 JOBS M/S TS USERS SYSAS INITS ACTIVE/MAX VTAM OAS 00024 00034 00015 00026 00190 00015/00065 00024 DVUSER2 ONLINE NSW J A=00AE PER=NO SMC=000 PGN=088 DMN=020 AFF=NONE CT=122.307S ET=590.945S WUID=JOB07991 USERID=DVUSER2 ADDR SPACE ASTE=13950B80 DSPNAME=CCA00003 ASTE=055A5300 DSPNAME=CCATEMP ASTE=033CCC80 DSPNAME=CCA00002 ASTE=055A5400 DSPNAME=CCA00001 ASTE=09A21100 DSPNAME=CCASERVR ASTE=033CC880