Contains a chunk of data cached in a disk cache
Description
A Vn file, or V file, holds a chunk of cached data on a client machine that is using a disk cache. In the name of an actual V file, n is
an integer; the name of each V file has a unique integer different from other V files on the machine (for example, V1, V2, and so on). The format of a V file depends on the format
of the data it is caching: a V file containing a cached binary file has a binary format; a V file storing a cached ASCII file has an ASCII format.
Each V file always resides in the cache directory, which by default is dcelocal/var/adm/dfs/cache. This directory is specified in the second field of the CacheInfo file; it can be overridden to name a different directory. The CacheItems file in the cache directory records information about each V file, such as its file ID and data version numbers.
The number of V files, or cache chunks, depends on the size of the disk cache (specified in the third field of the CacheInfo file, defined with the dfsd command's -blocks option, or set with the cm setcachesize command). For a disk cache, the number of chunks is heuristically computed as the number of cache blocks divided by 8. You can override the default number of chunks with the dfsd command using the -files option. Specify a positive integer not greater than 32,000.
To use a cache most effectively, issue the du command on the cache directory to determine the number of cache blocks used; compare this number to the number of blocks allocated to the cache. If you are not using 90 percent of the cache, increase the number of V files (chunks).
By default, each V file holds up to 65,536 bytes (64 kilobytes) of a cached file; files larger than 65,536 bytes are divided among multiple V files. A V file can hold only one cached element; if a cached element is smaller than the size of a V file (the chunk size), the remaining space in the V file remains unused.
You can override the default chunk size with the dfsd command using the -chunksize option. Specify an integer between 13 and 18 to be used as an exponent of 2; the unit of measure is bytes. For example, a value of 16 equals the default chunk size (2 to the 16th power equals 65,536). A value less than 13 or greater than 18 sets the chunk size to the default, as does a value of 16.
Cautions
Never directly modify or delete a V file; this can cause the kernel to panic. Always use the commands provided with DFS to alter the cache. If a V file is
accidentally modified or deleted, rebooting the machine should restore normal performance.
Related Information
Commands: cm setcachesize(8dfs)
Files: CacheInfo(4dfs)