6.1 Introduction to VOBs and VOB Administration

Any ClearCase development environment requires one or more VOBs. A VOB is the principal repository for ClearCase data and metadata. VOBs are a global resource; any VOB on the ClearCase LT server can be made accessible to any ClearCase user. Data can be centralized in a few VOBs, organized into multiple components at the VOB level, or distributed across a number of VOBs in other ways.

A typical VOB is created and populated with an initial collection of data by an administrator or project leader and accessed by many users. Significant administrative responsibilities associated with VOBs include the following:

• VOB creation and access control

• Importing data into a VOB from another source control system

• Backing up and recovering VOBs

• Relocating data from one VOB to another VOB

• Monitoring VOB integrity

• Moving, removing, and managing the storage used by VOBs

CAUTION: Moving a VOB is a complex procedure that requires several steps. You must follow these steps carefully or you risk losing or corrupting VOB data. See Chapter 11, Moving VOBs, for more information.

Rational ClearCase LT provides various VOB storage management tools as well as a job scheduler that can automate many routine VOB maintenance tasks. Chapter 16, Managing Scheduled Jobs, provides details on the job scheduler and related tools.

Types of VOBs

There are four types of VOBs. All have the same on-disk directory structure, and all have similar administrative requirements. You may not need all types at your site.

• Ordinary VOBs serve as the permanent repositories for data under ClearCase control. Most of the VOBs in a ClearCase network are ordinary VOBs. These VOBs are likely to consume more disk space and other server resources (memory, CPU cycles, and network bandwidth) than the other types of VOBs.

• Administrative VOBs allow centralized management of certain types of metadata that can be shared by other VOBs. Administrative VOBs are optional. See Chapter 8, Using Administrative VOBs and Global Types for more on this topic.

• UCM component VOBs, which function like ordinary VOBs but are treated by UCM as components used by a project.

• UCM project VOBs that store information about UCM artifacts such as projects, baselines, folders, and components. If your site does not use UCM, you will not need any UCM project VOBs. A UCM project VOB is the default administrative VOB for all of the UCM component VOBs that are included in the UCM projects stored in that VOB.

Access to VOB Data and Metadata

Users cannot access VOB data directly. They must access it using a view and refer to the VOB by its VOB-tag.

Views

Users access VOB data through views, which select specific versions of file and directory elements stored in the VOB and present them to a ClearCase LT user as part of the file system-a standard directory tree, whose top-level directory is called the VOB root directory. Users can also access VOB data and metadata using cleartool commands and ClearCase GUIs that do not need to use a view. Users cannot access VOB data directly.

Tags

ClearCase commands and utilities access a VOB by referring to its VOB-tag, which is a name with an associated global path that all ClearCase hosts can use to access the VOB. A VOB-tag is created whenever a VOB is created. All VOB tags are stored in the ClearCase registry, where they are accessible to all ClearCase LT hosts. Certain network configurations may require you to create additional tags or modify existing ones to ensure access to VOB data by all hosts.

VOB Server Processes

Access to VOB data is managed by several server processes that run on the ClearCase LT server:

• A db_server process handles requests from a single client program for access to any VOB on a ClearCase LT server.

• One or more vobrpc_server processes are started for each VOB on the ClearCase LT server. Each vobrpc_server process handles requests from one or more view_server processes.

• A vob_server process provides access to VOB storage pools. This process handles data-access requests from clients, forwarded to it by the vobrpc_server.

• A single lockmgr (lock manager) process manages transactions in the VOB databases of all VOBs on a ClearCase LT server

ClearCase Server Processes provides additional information on these and other ClearCase server processes.