9.1 VOB Server Configuration Guidelines

A host on which one or more VOB storage directories reside is a VOB host. A typical network distributes its VOBs among several VOB hosts. Nearly any host supported by ClearCase can be a VOB host (the exceptions are Windows Me and Windows 98). Selecting and configuring an appropriate VOB host are crucial to obtaining satisfactory ClearCase performance.

NOTE: ClearCase has special requirements for the Windows domain membership of VOB hosts, view hosts, and users. See Chapter 4, ClearCase and Windows Domains.

The computer chosen as a VOB host must satisfy these requirements:

• Main memory (RAM). The minimum recommended main memory size is 128 MB or half the size of all the VOB databases the server will host, whichever is greater. To this amount, add 7 MB of memory per VOB, regardless of VOB database size, as well as 750 KB of memory for any view_server process that will run on the VOB host. Adequate physical memory is the most important factor in VOB performance; increasing the size of a VOB host's main memory is the easiest (and most cost-efficient) way to make VOB access faster and to increase the number of concurrent users without degrading performance. For the best performance, configure the VOB host with enough main memory to hold the entire VOB database.

• Disk capacity. A VOB database must fit in a single disk partition, and VOB databases tend to grow significantly as development proceeds and projects mature. We recommend a high- performance disk subsystem, one with high rotational speed, low seek times, and a capacity of at least 10 GB.

If possible, use a RAID or similar disk subsystem that takes advantage of disk striping and mirroring. Mirrors are useful for backups, although there is a slight performance degradation associated with their use. However, striping helps overall performance and more than makes up for any degradation caused by mirroring. For more information, see Maximize Disk Performance.

• Processing power. A VOB host must have adequate CPU capacity. The definition of adequate in this context varies from one hardware architecture to another. With ClearCase and similar enterprise applications, server CPU capacity is a critical factor governing performance of client operations. Make the most of the available server CPU cycles by keeping nonessential processes-including ClearCase client tools and views-off the VOB host.

• Availability. A VOB intended for shared access must be located in a disk partition that is accessible to all ClearCase client hosts. Wherever possible, select a host that can be accessed with the same host name by all ClearCase hosts. (A host with multiple network interfaces presents a different name through each interface.) If a VOB host has multiple names, you must create multiple network regions, to logically partition the network.

See also Chapter 32, Improving VOB Host Performance.

VOB Feature Levels

A feature level is an integer that defines the set of features that a VOB supports. Whenever a ClearCase release introduces features that require support in the VOB database, you must raise the feature level of a VOB before clients can take advantage of the new features when accessing data in that VOB. The primary purpose of feature levels is to manage VOBs that are replicated (using ClearCase MultiSite) across server machines that are not all running the same ClearCase release.

Every ClearCase release is associated with a feature level. See the Release Notes for Rational ClearCase and ClearCase MultiSite for information on which feature levels a release supports.

Displaying the Feature Level

To display the feature level of a replica, use the Windows explorer or ClearCase Administration Console to display the properties of the VOB. The feature level is listed on the Custom tab. You can also use the cleartool command line.

To display the feature level of a replica family, use the command cleartool describe replica:replica-name@vob-tag. For example:

cleartool describe replica:tokyo@\dev
replica "tokyo"
created 20-Aug-00.13:35:37 by John Cole (jcole@goldengate)
replica type: unfiltered
master replica: sanfran_hub@\dev
...
feature level: 2
...

To display the feature level of a VOB family, use the command cleartool describe vob:vob-tag. For example:

cleartool describe vob:/vobs/dev
versioned object base "/vobs/dev"
created 15-Aug-00.14:19:03 by Susan Goechs (susan.user@minuteman)
master replica: boston_hub@/vobs/dev
replica name: boston_hub
VOB family feature level: 2
...

NOTE: Before you set the feature level for a newly created replica, its value is recorded as unknown. For example, if you use the describe command to show the properties of a new replica, the output looks like this:

cleartool describe replica:sanfran_hub@/vobs/dev
...
feature level: unknown

Changing the Feature Level

The chflevel command changes the feature level of a VOB. To raise the feature level of an unreplicated VOB:

1. Log on to the host that contains VOB storage directories for the VOBs you want to upgrade.

2. Issue the chflevel command with the -auto option. The command lists each VOB served by the host. It then offers to raise the feature level of each unreplicated VOB that is not already at the feature level corresponding to the release of ClearCase that is installed on the host.

When you use MultiSite, each VOB replica has a feature level, and the VOB family has a feature level. Replicas in the same family can have different feature levels. The family feature level is the feature level that is equal to or less than the lowest replica feature level found among members of the VOB family. Before you raise the feature level of a VOB family, you must raise the feature levels of all replicas in that family. For more information about feature levels and VOB replicas, see the Administrator's Guide for Rational ClearCase MultiSite.

VOB Schema Versions

Every VOB has a database schema version that denotes the format of the VOB database, and determines the types of data the VOB can accommodate. There are two schema versions:

• Schema version 53, which has been supported by every ClearCase release since 3.0, but is not supported by ClearCase LT

• Schema version 54, which provides better support for Windows security identifiers and is required when using ClearCase in an Active Directory environment. Schema version 54 also provides support for larger VOB database files (greater than 2 GB) on certain platforms.

All VOBs on a VOB server host must be formatted with the same schema version. When you install ClearCase server software on a host, you are prompted to select a schema version to be used by VOBs created on that host.

To change the schema version of an existing VOB to a higher-numbered schema version, use the reformatvob command. You cannot reformat a VOB to a lower-numbered schema version.