In the BEA WLS console, it's possible to define "T3 File Service". After googling about it, I was unable any practical info. Is it something useful ?
EDIT:
Deprecated since 6.1 ... a complete overview here , it's sad that no real alternative is provided.
The T3 protocol is (was) a proprietary network protocol for Java object serialization and RMI (before there even was an official RMI). It was used to communicate within a cluster of WebLogic servers (and between servers and clients).
It is deprecated now, so unless you know what you need it for, you probably do not need it.
The WebLogic file T3 service lets you provide high-speed, client-side access to native operating system files on the server.
Some people used it (with weblogic 6.1) to upload file attachments to an application in a cluster (in a C/S context I guess). Whether this was actually a good use case is another story.
Anyhow, the File Service has been deprecated in Weblogic 7.0, it just hasn't been removed for now (see the FileT3 in Weblogic 8.1 documentation or File T3 in Weblogic 10.0 documentation). If you need to write to the server file system, you'd better find another solution.