The most effective measures for ensuring good performance from VOB hosts are also the easiest to implement (technically, if not organizationally):

All the UNIX-based operating systems supported by ClearCase have a dynamic block buffer cache feature. As much main memory as possible is used to cache blocks of data files that have been updated by user processes. Periodically, the contents of the block buffer cache is flushed to disk.

This feature speeds up disk I/O significantly; making full use of it is a very important factor in good VOB host performance. An inadequate block buffer cache causes thrashing of VOB database files—the files in the db subdirectories of VOB storage directories). The result is a significant performance degradation, evidenced by:

We recommend that the size of a VOB host's block buffer cache average about 200% of the size of the host's largest VOB database file; the minimum acceptable size is about 50%. You cannot directly control the size of the block buffer cache; its size increases automatically when you add more main memory to the host.

If there is a substantial amount on non-ClearCase activity and/or ClearCase client activity on the host, you will need even more main memory to assure good VOB database performance.

% sar -b 60 5
12:14:22 bread/s lread/s  %rcache bwrit/s lwrit/s  %wcache pread/s pwrit/s
12:15:22       0       1      100       1       1        0       0       0
12:16:23       1       1      -60       2       2        0       0       0
12:17:24       0       4      100       4      17       77       0       0
12:18:25       0       6      100       3     145       98       0       0
12:19:25      17      91       81      28     335       92       0       0

12:19:25 bread/s lread/s  %rcache bwrit/s lwrit/s  %wcache pread/s pwrit/s
Average        4      21       83       8     100       92       0       0
   (cache-reads should be in the 90%–95% range)
   (cache-writes should be 75% or above)

Client workstations supporting a single user should have a minimum of 10–15 MIPS processing power, 16Mb of main memory, and 300Mb of disk storage. An additional 8–16Mb of main memory will further improve performance. Extra memory is especially recommended for users who run memory-intensive applications in the ClearCase environment, make extensive use of graphical user interfaces, or want their client workstations to serve double-duty as hosts for parallel distributed building.

The ClearCase default is to store all of a VOB's file system data in the default storage pools created by mkvob. These pools are located within the VOB storage directory. If a VOB host become I/O-bound, it is probably due to high storage pool traffic, caused by either “too many users” or “too many files”.

You can supplement (or replace) the default pools with remote storage pools, which effectively enable a VOB to outgrow its storage directory's disk partition. Remote pools need not be located on ClearCase hosts; they need only be accessible through NFS.

In some situations, remote storage pools can improve performance, as well:

This section describes procedures for reconfiguring the ClearCase multiversion file system (MVFS) on hosts running SunOS 4 or SunOS 5 (Solaris). By default, the MVFS is dynamically loaded at system startup with the following configuration:

You may wish to change the MVFS cache sizes to improve performance if your host performs builds that involve a large number of files, as indicated in Table 13-1.

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Note: Enlarging the MVFS caches reduces the amount of memory available to UNIX applications. If you use the “largeinit” MVFS configuration, you should also reconfigure each view that is used to access ClearCase data on that host, increasing its view_server cache size to 1Mb. See “Reconfiguring a View”.

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To change the MVFS cache sizes, perform one of the changes described below.