HP OpenVMS Systems Documentation

Content starts here HBMM Policy Specification Syntax
HP Volume Shadowing for OpenVMS: OpenVMS Version 8.4 > Chapter 8 Host-Based Minimerge (HBMM)

HBMM Policy Specification Syntax

An HBMM policy specification consists of a list of HBMM policy keywords enclosed within parentheses. The HBMM policy keywords are MASTER_LIST, COUNT, and RESET_THRESHOLD. Of the three keywords, only MASTER_LIST must be specified. If COUNT and RESET_THRESHOLD are omitted, the default values are supplied. For examples of policy specifications, see “How to Define an HBMM Policy” and the HP OpenVMS DCL Dictionary.

The use of these keywords and the rules for specifying them are described in this section.


The MASTER_LIST keyword is used to identify a set of systems as candidates for a master bitmap. The system-list value can be a single system name; a parenthesized, comma-separated list of system names; or the asterisk (*) wildcard character. For example:




When the system list consists of a single system name or the wildcard character, parentheses are optional.

An HBMM policy must include at least one MASTER_LIST. Multiple master lists are optional. If a policy has multiple master lists, the entire policy must be enclosed with parentheses, and each constituent master list must be separated by a comma, as shown in the following example:

(MASTER_LIST=(node1,node2), MASTER_LIST=(node3,node4))

There is no significance to the position of a system name in a master list.


The COUNT keyword specifies the number of master bitmap systems to be chosen from the systems listed in a master system list. Therefore, the COUNT keyword must be associated with a specific master list by enclosing both with parentheses.

A COUNT value of n means that you want master bitmaps on any n systems in the associated master list. It does not necessarily mean that the first n systems in the list are chosen.

The COUNT keyword is optional. When omitted, the default value is the number of systems in the master list or the value of six, whichever is less. You cannot specify more than one COUNT keyword for any one master list.

The following two examples are valid policies:

(MASTER_LIST=(node1,node2,node3),COUNT=2),(COUNT=2, MASTER_LIST=(system4,system5,system6))

The following example is not valid because the COUNT keyword is not grouped with a specific master list:

(MASTER_LIST=(node1,node2 ), MASTER_LIST=(node4,node5 ), COUNT=1) RESET_THRESHOLD=n

The RESET_THRESHOLD keyword specifies the number of blocks that can be set before the bitmap is eligible to be cleared. Each bit that is set in a master bitmap corresponds to a set of blocks that needs to be merged. Therefore, the merge time can be influenced by this value.

Bitmaps are cleared when the RESET_THRESHOLD is exceeded, although the reset is not guaranteed to occur immediately when the threshold is crossed. For additional information about choosing a value for this attribute, see “Considerations for Setting a Bitmap RESET_THRESHOLD Value” and “Volume Shadowing Parameters ”.

A single reset threshold value is associated with any given HBMM policy. Therefore, the RESET_THRESHOLD keyword cannot be specified more than once in a given policy specification. Because its scope is the entire policy, the RESET_THRESHOLD keyword cannot be specified inside a constituent master list when the policy uses multiple master lists.

When the RESET_THRESHOLD keyword is omitted, the value of 1,000,000 is used by default.

The following policy example includes an explicit reset threshold value: