Disaster Tolerance and Recovery in a Serviceguard Cluster
Disaster Tolerant Architecture Guidelines
depending on the volume of data. Some applications, depending on the role they play in the business, may need to have a faster recovery time, within hours or even minutes.
On-line Data Replication
Data can be replicated either synchronously or asynchronously. Synchronous replication requires one disk write to be completed and replicated before another disk write can begin. This method improves the chances of keeping data consistent and current during replication. However, it greatly reduces replication capacity and performance, as well as system response time. Asynchronous replication does not require the primary site to wait for one disk write to be replicated before beginning another. This can be an issue with data currency, depending on the volume of transactions. An application that has a very large volume of transactions can get hours or days behind in replication using asynchronous replication. If the application fails over to the remote site, it would start up with data that is not current.
Currently the two ways of replicating data
Physical Data Replication
Each physical write to disk is replicated on another disk at another site. Because the replication is a physical write to disk, it is not application dependent. This allows each node to run different applications under normal circumstances. Then, if a disaster occurs, an alternate node can take ownership of applications and data, provided the replicated data is current and consistent.
As shown in Figure
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