Minicopy Restrictions

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. If you attempt to use earlier versions of OpenVMS in the cluster, the minicopy feature is disabled.

The 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 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 have a bitmap for each shadow set member. When you return each disk to the shadow set, you can 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 bitmap is not created.

Unused 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 bitmaps with the DELETE command, as described in “Deleting Bitmaps”.

Misleading error message

When you attempt to start a 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 are deleted cannot use a minicopy operation. Instead, a full copy is performed.

If a shadow set member leaves the set because of an error or timeout, a bitmap is not available. A bitmap is only available for a minicopy when a shadow set member is explicitly dismounted.

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 (Alpha Only)”.