OpenVMS Version 7.3 introduced
four system parameters for managing minicopy bitmap messages. The
four parameters apply equally to managing HBMM bitmap messages. Three
parameters are used to manage update traffic between a master bitmap
and its corresponding local bitmaps in an OpenVMS Cluster system.
The fourth parameter controls whether bitmap system messages are sent
to the operator console and, if they are to be sent, the volume of
messages. System parameters are dynamic; they can be changed on a
running system. Table 3-4 lists the bitmap system parameters.
The bitmap system parameters
check if the messages are buffered and then packaged in a single System
Communications Services (SCS) message to update the master bitmap
or whether each message is sent immediately. The system parameters
are used to set the upper and lower thresholds of message traffic
and a time interval during which the traffic is measured.
The writes issued by each
remote node are, by default, sent one at a time in individual SCS
messages to the node with the master bitmap. This is known as single-message mode.
If the writes sent by a remote
node reach an upper threshold of messages during a specified interval,
the single-message mode switches to the buffered-message
mode. In the buffered-message mode, messages (up to nine)
are collected for a specified interval and then sent in one SCS message.
During increased message traffic, grouping multiple messages in one
SCS message is more efficient than sending each message separately.
Table 3-4 Bitmap System Parameters
Parameter | Meaning | Unit | Min | Max[1] | Default |
|---|
WBM_MSG_INT | In single-message mode, the time interval
between assessment of the most suitable bitmap message mode. In buffered-message
mode, the maximum time (in milliseconds) that a message waits before
it is sent. | msec | 10[2] 1[3] | -1[2] 100[3] | 10[2] 7[3] |
WBM_MSG_UPPER | The upper threshold for the number
of messages sent during the test interval (calculated in 100 millisecond
windows) that initiates buffered-message mode. | msgs/interval | 0 | -1 | 80 |
WBM_MSG_LOWER | The lower threshold for the number
of messages sent during the test interval (calculated in 100 millisecond
windows) that initiates single-message mode. | msgs/interval | 0 | -1 | 20 |
WBM_ OPCOM_ LVL | Controls whether
bitmap messages are provided to the operator console: 0 means messages
are turned off; 1 means messages are provided when bitmaps are started,
deleted, and renamed, and when the SCS message mode (buffered or single)
changes; 2 means that all messages for a setting of 1 are provided
along with detailed messages for debugging purposes. | n/a | 0 | 2 | 1 |
Setting System Parameters |
 |
To set
or modify volume shadowing parameters, edit the [SYSn.SYSEXE]MODPARAMS.DAT file or the appropriate AUTOGEN include file.
After editing the file, execute SYS$UPDATE:AUTOGEN as described in
the HP OpenVMS System Manager's Manual, Volume 2: Tuning, Monitoring,
and Complex Systems. If you have an OpenVMS Cluster system, ensure
that the system parameters are updated on each node. Example 3-2 illustrates a MODPARAMS.DAT file that includes
assignment statements to set shadowing parameters.
Example 3-2 MODPARAMS.DAT File
.
! Volume Shadowing Parameters:
SHADOWING=2 ! Enables phase II shadowing
SHADOW_SYS_DISK=1 ! Enables system disk shadowing
SHADOW_SYS_UNIT=7 ! Specifies 7 as the virtual unit number
of the system disk
SHADOW_MAX_COPY=4 ! Specifies that 4 parallel copies can occur at one time
SHADOW_MBR_TMO=120 ! Allows 120 seconds for physical members to fail over
! before removal from the shadow set
. |
See the HP OpenVMS System Manager's Manual, Volume
2: Tuning, Monitoring, and Complex Systems for complete information
about invoking AUTOGEN and specifying the appropriate command qualifiers
to perform the desired AUTOGEN operations.
Displaying System Parameters |
|
It is sometimes useful to use the SYSGEN command SHOW
to display the values of system parameters. You do not need special
privileges to invoke the SYSGEN utility. You can use either a qualifier
or the name of a system parameter with the SHOW command, or you can
use the SHOW/ALL command to display information about all system parameters.
(Enter HELP SHOW at the SYSGEN> prompt for more information about
the SHOW command.) The following example illustrates how you can check
the current default, minimum, and maximum values for the SHADOWING
parameter.
$ MCR SYSGEN
SYSGEN> SHOW SHADOWING
Parameter Name Current Default Min. Max. Unit Dynamic
-------------- ------- ------- ------- ------- ---- -------
SHADOWING 2 0 0 2 Coded-valu
SYSGEN>
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