Veritas Volume Replicator (VVR) offers different modes of replication, synchronous and asynchronous. Bunker replication enables you to combine the advantages of synchronous and asynchronous replication, without the overhead of maintaining two complete copies of your data on two Secondary sites.
Bunker replication maintains a copy of the Primary SRL on a site near the Primary site, known as the bunker site. The copy of SRL can be used to bring the Secondary up-to-date if there is a disaster at the Primary site. Bunker replication only requires additional storage for the bunker SRL. The bunker SRL is usually replicated using synchronous mode to provide zero data loss. Ideally, the bunker SRL should be in a site sufficiently far away to not be within the same disaster zone as the Primary site, yet close enough to not impede the synchronous update of the bunker SRL. If both the Primary and the bunker are lost, the Secondary must start from a previous point in time. Therefore, choose the bunker site so that the likelihood of this is rare.
Bunker replication can be performed using an IP network or using direct connectivity to the storage, such as IP over Fiber Channel, Direct Attached Storage (DAS) or Network Attached Storage (NAS). If replication is performed over IP, the Primary host sends writes to a host at the bunker site, known as the bunker host. The bunker host performs writes to the bunker SRL. If replication is done with direct storage, the disk group containing the bunker SRL is imported on the Primary host and the Primary host performs writes to both the bunker SRL and the Primary SRL.