Understanding the Architecture of MultiSite


The following sections describe the MultiSite architecture.

Replicated VOB Databases

A VOB provides permanent storage for an entire directory tree: directories, files, and links. The historical versions of the files in the VOB are stored in data container files in storage pool directories. The VOB database records the evolution of the version-controlled file system objects and stores the associated metadata, including version labels, hyperlinks, configuration records, and so on. For more information about VOB data structures, see the ClearCase documentation set.

If MultiSite is not used, each VOB has a single set of data containers and a single database. With MultiSite, some or all VOBs are replicated. A replicated VOB is located at multiple sites; at each site is a copy of the VOB, called a VOB replica. Collectively, the set of replicas of a VOB is called a VOB family. Each replica includes a full set of data containers and a complete copy of the VOB database. At its site, a replica appears to be a regular VOB; developers can check out, edit, and check in; build software; attach metadata annotations to objects; and so on. Regular ClearCase use models apply to use of replicas, but there are some coordination issues that administrators must consider. (For more information, see Planning a MultiSite Implementation.) Also, MultiSite features allow simultaneous development to occur at different replicas without conflicts. Enabling Independent Development: Mastership describes how conflict avoidance works.

For more information, see VOBs and VOB Replicas, VOB Objects and VOB Replica Objects and ClearCase Commands Related to MultiSite.

MultiSite Terminology

MultiSite documentation uses the following terms.

Term
Definition
Replica
A copy of a VOB. To refer to a VOB replica, use its replica name and VOB tag.
Family
All the replicas of a VOB. The family name of a VOB family is the VOB tag.
Site
The collection of clients and servers known to a registry host. Each site can contain at most one replica of a VOB.
Host
The LAN name or IP address of the network node that contains the database of the VOB replica.