HP OpenView Storage Mirroring User Guide (360226-002, May 2004)

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Understanding the Double-Take Source Connection
resource
The Double-Take Source Connection resource is like other cluster resources. The cluster controls the movement from node
to node if there is a failure. This resource additionally controls the Storage Mirroring connection. Therefore, if there are node
failures, the Storage Mirroring connection is automatically handled by the new owning node without user intervention.
When you are first setting up your Storage Mirroring configuration or when troubleshooting, you may want to understand
what the resource is doing. When the Double-Take Source Connection resource is brought online or taken offline a command
shell environment is created and a Storage Mirroring DTCL script is executed. The script either establishes a Storage
Mirroring connection or disconnects the Storage Mirroring connection, depending on the node. If you are using the
Double-Take Source Connection resource, the cluster object will control these scripts as the cluster service switches
between nodes. If you do not use the Double-Take Source Connection resource, there is no mechanism to bring a Storage
Mirroring connection online. The non-owning node does not know that a connection was present because the connection
information stored in the connect.sts is not replicated between systems. Therefore, if that non-owning node becomes the
owner, the connection would need to be manually re-established. So it is important to always use the Double-Take Source
Connection resource when the source is a cluster configuration.
Outlined briefly below are the steps used in the DTCL online and offline scripts.
Online Script
1. Identify the elements used in the script: source, target, replication set, and so on.
2. Login to the target.
3. Specify the source.
4. Establish a connection from the source to the target using identical drive mappings on the target as on the source.
5. Begin a block checksum mirror.
The source will replicate changes to the data after the mirror completes.
Offline Script
1. Identify the elements used in the script: source, target, replication set, and so on.
2. Login to the target.
3. Specify the source.
4. Determine the connection ID and disconnect it.
If you want to view the DTCL script files directly, they are called
online.dtcl and offline.dtcl and are located in the
directory where you installed Storage Mirroring. These are text files that can be viewed with any text editor.
NOTE:
Notice that identical drive mappings are used in the online script. If your source and target do not have
the same drive letters, the online script will fail.
NOTE:
Making changes to the online.dtcl or offline.dtcl scripts is not recommended. Those users who are
experienced and comfortable creating and editing Storage Mirroring scripts may want to modify them on their
own. Such modifications may not be supported by technical support.