HP StorageWorks SAN Virtualization Services Platform Manager User Guide (5697-0454, May 2010)

enables you to transfer production from a virtual disk to a mirror of the virtual disk without losing
application data.
Split is enabled only under the following conditions:
• No host has permission to access the source element of the async mirror group on which you
perform the split.
• The next to last PiT created on the group was fully copied to all task destinations.
• The last PiT created on the group is empty. There were no data modifications on the group since
the last PiT was created. If there had been, this PiT would have stored these modifications and
would not be empty.
• The group is suspended.
Therefore, before splitting an async mirror group:
1. Stop the applications that are using the async mirror group source element.
2. Unmount the virtual disk on the host side. All host application updates are now flushed to the
virtual disks.
3. Remove all host presentations from the group source element. To do this, you need either to
disconnect the hosts from the VSM server or power them down and then delete the hosts from
the hosts list (which you can access from the Host node in the tree).
4. Create a user PiT on the group source element. The PiT is created, but does not include any
modification since there is now no host that can access the group source element.
5. Wait until the user PiT is fully copied to the destination domain.
6. Suspend the group.
To split an async mirror group:
1. Right-click the group.
2. Select Manage > Split. A confirmation screen appears.
3. Click Finish. The group is split.
Merging an async mirror group
Merge is an operation that you can perform on a virtual disk or VDG that reestablishes an async
mirror group that was split or detached. When you merge a group, you identify an existing virtual
disk as the source virtual disk and another existing virtual disk as the destination virtual disk. The
mirror service creates a new group, resuming mirroring from the newest PiT that is identical on the
source and destination. This feature enables you to reverse the direction of mirroring, by using the
former destination virtual disk of a split group as the source virtual disk of the new group and identifying
the former source as the new destination.
The mirror service checks that the newest PiT on the new source virtual disk and the newest PiT on the
new destination virtual disk are both empty and have identical timestamps. If these conditions are not
all satisfied, the merge fails and an event is written to the event log describing which condition failed.
If you are trying to reestablish an async mirror group between elements of an async mirror group that
was properly split, the last PiT copied from the source to the destination is empty and the merge
succeeds.
If you want to merge a virtual disk after detaching an async mirror group, the last PiT on the source
and destination may not be empty. You can perform a merge, allowing the mirror service to rollback
to a PiT earlier than the newest PiT on the destination, if necessary, in order to create a new group.
This stops the merge from failing if the most recent PiT is not empty. In this case, the mirror service
finds the most recent PiT on the destination that is synchronized with a PiT on the source and rolls
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