A DFS client machine serves primarily as a single or multiuser workstation. It communicates with File Server machines to access files for application programs, provides local data storage, and provides computer cycles. A domain should include enough client machines to allow its users to access exported data from the local or foreign cells.
Each client machine must run
· The Cache Manager, which is initialized by the dfsd process, in the kernel
· The dfsbind process
The Cache Manager runs as part of the client machine's kernel. It communicates with server processes running on File Server machines to fetch data on behalf of application programs. When an application program on a client machine requests data, the Cache Manager contacts the FL Server to learn the location of the fileset that houses the data. It then translates the application program's data request into a Remote Procedure Call (RPC) to the File Exporter running on the appropriate File Server machine.
When the Cache Manager receives the requested data, it stores the data in its local cache, which is an area reserved for data storage on disk or in memory on the client machine. It then passes the data to the application program. The Cache Manager also stores tokens it receives from the File Exporter on the File Server machine.
Within limits, the Cache Manager attempts to make the most current data available to users. The Cache Manager judges the currency of the data in its cache based on the type of fileset from which the data was retrieved:
· If the data comes from a read/write fileset, the Cache Manager uses the tokens to track the currency of the data. The cached data remains current for as long as the Cache Manager's tokens remain valid. If the read/write source of the data changes, the File Exporter revokes the tokens. The next time the data is requested, the Cache Manager retrieves the newer version to its cache before providing it to the application program.
· If the data comes from a read-only fileset, the Cache Manager compares the amount of time since the data was last verified as being current with a configurable time period associated with the fileset. If the read-only copy of the data changes, the Cache Manager continues to distribute the cached data until the time since verification equals or exceeds the configurable time period. The next time data is requested, the Cache Manager retrieves the newer version to its cache before providing it to the application program.
The dfsd process initializes the Cache Manager on a client machine. It can be used to alter aspects of the Cache Manager's cache, such as its location and size. It also starts several background daemons, which help the Cache Manager manage the data stored in its cache.
The dfsbind process, in addition to its role on File Server machines, is used by the Cache Managers on client machines to help with the resolution of DCE path names. It also obtains authentication information about users that Cache Managers require for RPC bindings to File Server machines. (See Client Machine Processes and Files for more information about the Cache Manager and the dfsd and dfsbind processes.)