Cascading Failover in a Continentalclusters, December 2005

replication group and the replication group from the secondary site to the recovery site is referred to
as the recovery replication group.
The following are three actions used to perform data replication specific operations.
• Establish: To “establish” a replication group or the replication link refers to enabling data to
be replicated from source to the destination or vice versa. This sometimes involves a block or
track level copy to the out of date copy and thus while copying is going on, the device being
replicated to is inconsistent. Unless stated, the data is copied from source to the destination.
• Split: To “split” a replication, the data replication link, or the local mirror refers to stopping
the data replication from source to destination or from a device to a local mirror.
• Restore: To “restore” refers to copying data from a local mirror to a device in the
replication group.
Audience
It is assumed that readers are already familiar with Serviceguard configuration tasks,
Continentalclusters installation and configuration procedures, HP StorageWorks XP, EMC Symmetrix,
BC, BCV, XP CA, SRDF, XP CA and Symmetrix multi-hop concepts, and configuration and usage of
the Raid Manager command line interface and Symmetrix Command Line Interface (SymCLI).
Configuration
Cluster and Storage Requirements
Most physical data replication technologies have the option to perform automatic link recovery. The
automatic link recovery provides the ability synchronize data from source to destination devices when
the data replication links have been recovered. For the cascading failover solution, this option to
automatically recover links should be “disabled”. This will keep the links from automatically trying to
establish a new connection upon failure of all links. This is required to allow the time to split the local
mirror on the secondary disk array (device B’) and the recovery replication group before re-
establishing the data replication for the primary replication group (that is between the primary disk
array and the secondary disk array upon link recovery).
Other than what has been stated above, there are no additional cluster or storage requirements
besides what is required by the Continentalclusters product.
Volume Group Setup
Use the following procedure to set up volume groups for the devices used on the disk arrays.
Currently, LVM and VxVM volume management software suites are supported for this configuration.
Please refer to LVM and VxVM documentation for specific commands.
1. Before creating the volume groups, make sure that the data replication link is established
between the primary devices on the primary disk array and the destination devices on the
secondary disk array (i.e. devices A and B), and the local mirror device (device B’) in the
secondary disk array are established as mirrors of the local standard devices.
2. Create the volume group only on one cluster node that connects to the primary disk array.
3. For LVM and VxVM, metadata needs to be replicated to the destination devices (devices C
and C’) in the recovery disk. The following are steps to replicate data to the recovery site.
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