When a user downloads a file (usually by a check out or copy out operation), the gateway cache is queried to determine if an up-to-date copy of the file resides in the cache. (The gateway will check with the upstream storage server to determine if the cache copy is up-to-date). If the cache copy is nonexistent, or stale, the cache copy will be refreshed from the storage server, and the file data will be sent to the client workstation. This is referred to as passive caching, or caching on demand.
If DFT is enabled on the gateway server (it is on by default) then DFT will be used to synchronize the gateway cache copy of the file to the master file on the storage server. If DFT is enabled for the client, then DFT will also be used to synchronize the cache copy to the client workstation copy. (There is no guarantee that the cache copy and the client copy differ in the same way, and thus distinct synchronization operations are required for each step of the file transfer process.)
If DFT is disabled on the gateway server, then the entire contents of the master copy of the file will be transferred to the gateway cache and the client. (The cache is updated as the file data passes through the gateway server.) This can be quite inefficient when working with large files that may have only accumulated a relatively small number of changes; thus, it is usually preferred that DFT remain enabled on servers.