Technical data

System Management Features
4.12 New System Parameters
WBM_MSG_LOWER is the lower threshold for the number of messages sent
during the test interval that initiates single-message mode. In single-message
mode, the writes issued by each remote node are, by default, sent one by one in
individual SCS messages to the node with the master write bitmap. If the writes
sent by a remote node reach an upper threshold of messages during a specified
interval, single-message mode switches to buffered-message mode.
The minimum value of WBM_MSG_LOWER is 0 messages per interval. The
maximum value is -1, which corresponds to the maximum positive value that a
longword can represent. The default is 10.
WBM_MSG_LOWER is a DYNAMIC parameter.
4.12.14 WBM_MSG_UPPER
WBM_MSG_UPPER is one of three system parameters that are available for
managing the update traffic between a master write bitmap and its corresponding
local write bitmaps in an OpenVMS Cluster system. (Write bitmaps are used
by the volume shadowing software for minicopy operations.) The others are
WBM_MSG_INT and WBM_MSG_LOWER. These parameters set the interval
at which the frequency of sending messages is tested and also set an upper and
lower threshold that determine whether the messages are grouped into one SCS
message or are sent one by one.
WBM_MSG_UPPER is the upper threshold for the number of messages sent
during the test interval that initiates buffered-message mode. In buffered-
message mode, the messages are collected for a specified interval and then sent
in one SCS message.
The minimum value of WBM_MSG_UPPER is 0 messages per interval. The
maximum value is -1, which corresponds to the maximum positive value that a
longword can represent. The default is 100.
WBM_MSG_UPPER is a DYNAMIC parameter.
4.12.15 WBM_OPCOM_LVL
WBM_OPCOM_LVL controls whether write bitmap system messages are sent to
the operator console. (Write bitmaps are used by the volume shadowing software
for minicopy operations.) Possible values are shown in the following table:
Value Description
0 Messages are turned off.
1 The default; messages are provided when write bitmaps are started, deleted,
and renamed, and when the SCS message mode (buffered or single) changes.
2 All messages for a setting of 1 are provided plus many more.
WBM_OPCOM_LVL is a DYNAMIC parameter.
4.13 Volume Shadowing for OpenVMS
Volume Shadowing for OpenVMS introduces three new features, the minicopy
operation enabled by write bitmaps, new qualifiers for disaster tolerant support
for OpenVMS Cluster systems, and a new /SHADOW qualifier to the INITIALIZE
command. These features are described in this section.
System Management Features 4–19