Planning and Configuring Replication

To set up an efficient VERITAS^™ Volume Replicator (VVR) configuration, it is necessary to understand how the various VVR components interact with each other. This chapter explains the interactions and presents the decisions you must make when setting up a VVR configuration. The chapter Tuning Replication Performance explains performance considerations. This document assumes that you understand the concepts of VVR. For more information, read the description of concepts in the VERITAS Volume Replicator Administrator's Guide.

In an ideal configuration, data is replicated at the speed at which it is generated by the application. As a result, all Secondary hosts remain up to date. A write to a data volume in the Primary flows through various components and across the network until it reaches the Secondary data volume. For the data on the Secondary to be up to date, each component in the configuration must be able to keep up with the incoming writes. The goal when configuring replication is that VVR be able to handle temporary bottlenecks, such as occasional surges of writes, or occasional network problems.

If one of the components cannot keep up with the write rate over the long term, the application could slow down because of increased write latency, the Secondary could fall behind, or the SRL might overflow. If a component on the path that completes the write on the Primary cannot keep up, latency might be added to each write, which leads to low application performance. If other components, which are not on this path, cannot keep up with the write rate, it is likely that the writes on the Primary proceed at their normal pace but accumulate in the SRL. As a result, the Secondary falls behind and the SRL eventually overflows. Therefore, it is important to examine each component to ensure that it can support the expected application write rate.

In this document, the term application refers to the program that writes directly to the data volume. If a database is using a file system mounted on a data volume, the file system is the application; if the database writes directly to a data volume, then it is considered the application. For information about the VVR concepts, refer to the VERITAS Volume Replicator Administrator's Guide.