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
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
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:
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:
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:
(MASTER_LIST=*, COUNT=4, RESET_THRESHOLD=800000)