/POLICY=HBMM[=policy-name]
/POLICY=HBMM[=policy-specification]
Note: This qualifier applies to HBMM operations only. If you
specify any non-HBMM qualifiers with this one, the command will
fail.
Creates or deletes a policy for host-based minimerge (HBMM).
HBMM is the only supported value for the /POLICY qualifier, and
it must be included. You can optionally specify a named policy,
including DEFAULT, or you can specify NODEFAULT to indicate
that the shadow set to which it is applied is not to use HBMM,
including any DEFAULT policy. For details about specifying
policies and using the DEFAULT and NODEFAULT policy names, see
the VSI Volume Shadowing for OpenVMS manual.
When /POLICY is specified with /DELETE, it removes either a
specified HBMM named policy or the HBMM policy for a specific
shadow set. You cannot delete the NODEFAULT policy.
When /POLICY is specified with /NAME, it defines a clusterwide
named policy. When no qualifiers other than /NAME or /DELETE are
specified, /POLICY defines a policy for a specific shadow set.
Deleting bitmaps with the DELETE/BITMAP command causes a bitmap
to be deleted. However, the shadowing software recognizes this
condition and starts a new bitmap immediately. To disable HBMM
bitmaps, you have to use the command SET SHADOW/DISABLE=HBMM.
When defining a policy, you use five keywords (MASTER_LIST,
COUNT, RESET_THRESHOLD, MULTIUSE, and DISMOUNT) to control
the placement and management of HBMM bitmaps. An HBMM policy
specification consists of a list of these keywords enclosed
within parentheses. Only the MASTER_LIST keyword is required.
If COUNT and RESET_THRESHOLD are omitted, default values are
applied.
The MULTIUSE and DISMOUNT keywords specify the number of bitmaps
to be converted to multiuse bitmaps during the automatic and
manual removal of members respectively. If MULTIUSE is omitted,
then automatic minicopy on volume processing is not enabled.
As a result, no HBMM bitmap is converted to multiuse bitmap. If
DISMOUNT is omitted, only a maximum of 6 HBMM bitmaps can be used
as multiuse bitmaps.
o MASTER_LIST=list
The MASTER_LIST keyword is used to identify a set of systems
as candidates for a master bitmap. The list value can be a
single system name; a parenthesized, comma-separated list
of system names; or the wildcard character, as shown in the
following examples:
MASTER_LIST=NODE1
MASTER_LIST=(NODE1,NODE2,NODE3)
MASTER_LIST=*
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.
o COUNT=n
The COUNT keyword specifies how many systems in the master
list can have master bitmaps. Therefore, the COUNT keyword and
its associated MASTER_LIST must be enclosed within a single
parenthetical statement.
The COUNT value specifies the number of systems on which you
want master bitmaps. It does not necessarily mean that the
first n systems in the list will be chosen.
When the COUNT keyword is omitted, the default value is 6
or the number of systems in the master list, whichever is
smaller.
You cannot specify more than one COUNT keyword per master
list.
Examples:
(MASTER_LIST=(NODE1,NODE2,NODE3), COUNT=2)
(MASTER_LIST=(NODE1,NODE2,NODE3),COUNT=2),(COUNT=2,MASTER_LIST=(NODE4,NODE5,N
NODE6))
o 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 set bit in a master bitmap corresponds to a set of blocks
to be merged, so this value can affect the merge time.
Bitmaps are eligible to be cleared when the RESET_THRESHOLD
is exceeded. However, the reset is not guaranteed to
occur immediately when the threshold is crossed. For more
information about choosing a value for this attribute, see the
VSI Volume Shadowing for OpenVMS manual.
The reset threshold is associated with a specific HBMM policy,
so the RESET_THRESHOLD keyword can be defined only once in a
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. See the following example:
(MASTER_LIST=*, COUNT=4, RESET_THRESHOLD=1000000)
Example:
The command in the following example defines the HBMM named
policy POLICY_2, which has two master lists. Having multiple
master lists can be useful in a multiple-site OpenVMS Cluster
configuration because a policy can be defined to ensure that
at least one surviving system has an HBMM bitmap in the event
of an outage at one or more sites.
$ SET SHADOW /POLICY=HBMM=( -
_$ (MASTER_LIST=(NODE1,NODE2,NODE3), COUNT=2), -
_$ (MASTER_LIST=(NODE4,NODE5,NODE6), COUNT=2), -
_$ RESET_THRESHOLD=150000) -
_$ /NAME=POLICY_2
In a policy with multiple master lists, a given system name
can appear in only one master list.
A shadow set need not be mounted to have an HBMM policy
defined for it.
See the SET SHADOW Examples help topic for several more
/POLICY examples. For more information about HBMM policies,
see the VSI Volume Shadowing for OpenVMS manual.
o MULTIUSE=n
The MULTIUSE keyword enables automatic minicopy on volume
processing. n specifies the number of existing HBMM master
bitmaps to be converted to multiuse bitmaps in the event that
a shadow set member is removed from the shadow set by the
shadowing driver.
During a loss of connectivity to a site or controller,
shadowing may remove a member from the shadow set. When the
member is added back to the shadow set, a full shadow copy
occurs.
By converting a few of the HBMM bitmaps to multiuse, all
writes that are performed to the shadow set are recorded.
Thus, when the member is added back to the shadow set, the
multiuse bitmap can be used for a minicopy operation. This is
much faster than a full copy operation.
The value of n cannot exceed the implied or explicit value
of COUNT. If MULTIUSE is not specified, then bitmaps are not
converted to multiuse and a full copy operation is required.
Fatal drive errors that remove a shadow set member do not
cause a multiuse conversion as the drive has to be replaced
and therefore requires a full copy operation.
o DISMOUNT=n
The DISMOUNT keyword allows all the 12 write bitmaps to be
used by Shadowing as multiuse bitmaps, thereby reducing the
single point of failure of single minicopy master bitmaps.
n specifies the number of HBMM bitmaps to be converted to
multiuse bitmaps every time a member is dismounted from a
shadow set with the following command:
DISMOUNT/POLICY=MINICOPY