The following restrictions apply to the use of minicopy:
Minicopy can be used in an OpenVMS
Cluster only when all nodes in the cluster are running either OpenVMS
Alpha Version 7.2--2 or OpenVMS Version 7.3 (or later), or a combination
of these versions. OpenVMS VAX Version 7.3 can support and contribute
to the bitmap that is mastered by an OpenVMS Alpha node. If you
attempt to use earlier versions of OpenVMS in the cluster, the minicopy
feature is disabled.
The write bitmap can be used only once. For example, if you dismount a three-member shadow set consisting
of D1, D2, and D3, and you then mount only D1 with the /POLICY=MINICOPY[=OPTIONAL]
qualifier, a write bitmap is created. When you mount either D2 or
D3 back into the shadow set, a minicopy is performed. When you mount
the remaining member into the shadow set, a full copy is performed. To avoid the requirement of a full copy on the second member,
dismount shadow set members one at a time, using /POLICY=MINICOPY
for each. In that way, you will have a write bitmap for each shadow
set member. When you return each disk to the shadow set, you will
be able to do a minicopy for each.
You cannot prioritize which member is updated by
a minicopy operation if you specify two members in the same MOUNT
command. To ensure that the minicopy occurs immediately, specify only
one shadow set member in each MOUNT command. Wait for the minicopy
to start, then add the next member with another MOUNT command.
If a shadow set is already marked by the volume
shadowing software for a merge operation, the merge operation occurs,
and a write bitmap is not created.
Unused write bitmaps for a virtual unit remain in
memory when the virtual unit is dismounted. When the virtual unit
is mounted again, they are automatically deleted. You can delete excess write bitmaps with the DELETE command,
as described in
Deleting Write Bitmaps.
Misleading error message When you attempt to start a write bitmap and dismount a shadow
set member (with DISMOUNT/POLICY=MINICOPY[=OPTIONAL]), the following
error message is displayed if the shadow set member is in a merge
operation or is a copy target:
%DISM-F-SRCMEM, only source member of shadow set cannot be dismounted
A more meaningful error message is planned for a future version
of minicopy.
If a node with one or more master bitmaps shuts
down or crashes, the bitmaps on the node are deleted. Therefore,
the shadow sets whose master bitmaps were deleted will not be able
to use a minicopy operation. Instead, a full copy will be performed.
If a shadow set member leaves the set because of
an error or timeout, a write bitmap will not be available. A write
bitmap is only available for a minicopy when a shadow set member
is explicitly dismounted.
If you intend to use the minicopy feature in a mixed-architecture
OpenVMS Cluster system, HP advises you to set the SHADOW_MAX_COPY
system parameter to zero on all VAX systems. This setting prevents
a copy from being performed on a VAX when the intent was to perform
a minicopy on an Alpha. In a mixed-architecture cluster, it is possible,
although highly unlikely, that a VAX system could be assigned the
task of adding a member to a shadow set. Because a VAX system cannot
perform a minicopy, it would perform a full copy instead. Fo information
about SHADOW_MAX_COPY, see
Volume Shadowing Parameters.
For systems running OpenVMS Alpha Version 7.2-2
or 7.3, additional steps are required to access the dump file from
a system disk shadow set in which a minicopy operation was used
to return a member to the shadow set. For more information, see
Obtaining Dump Files of Shadowed System Disk When Minicopy Is Used.