InfoScale™ 9.0 Replication Administrator's Guide - AIX

The role of the logowner

To use the Secondary in a disaster recovery scenario, the order of writes (write-order fidelity) must be maintained. When replicating in shared disk-group environment, VVR maintains the order of writes by designating one node in the cluster as the logowner. The logowner manages the writes to the SRL on the Primary. The writes are handled differently depending on whether the replication is set to synchronous or asynchronous.

For synchronous RLINKs, all writes are performed on the logowner; writes issued on nodes other than the logowner are sent over the cluster network to the logowner, to be performed there. This process is called write shipping.

For asynchronous RLINKs, the writes are performed on the node where they are issued. However, before writing to the SRL, the node sends a request to the logowner. The logowner responds with a message indicating the position in the SRL that was assigned for that write. After receiving the response from the logowner, the node writes to the SRL and then to the data volumes. This process is called metadata shipping. The information about the position in the SRL and how much space is allocated is known as metadata. If an RVG has both synchronous and asynchronous RLINKs, the RVG uses write shipping.

The logowner also is responsible for replicating the writes for the entire cluster to the Secondary site. If the RLINK is using metadata shipping, the logowner must read back the writes from the SRL before sending the writes to the Secondary.

The master is the default logowner. The logowner follows the CVM master on a master switch.

To optimize the master node workload you can choose to modify the default settings and assign the log owner role to any other cluster node (slave node).

For assigning a slave node as a logowner,

See Assigning a slave node as a logowner.