From Linux NFS
A FedFS domain root directory is the top-level directory of a FedFS domain. It is what is visible when a FedFS-enabled client mounts the top of a FedFS domain namespace. Typically a FedFS-enabled NFS client mounts the directory at /nfs4/fedfs-domain-name .
A FedFS domain root usually contains nothing but junctions that refer clients to file servers that hold more interesting content, like user directories. The domain root is simply a starting point for accessing the rest of a domain's name space.
This article describes an easy way to set up a FedFS domain root on a Linux NFS server.
Select one or more NFS servers to host the domain root export
The domain root directory typically sees little traffic, particularly since an individual domain root directory contains little data. However, clients depend on the domain root directory being available to access all other files in a FedFS domain. A server with high availability is recommended for this role.
The NFS server you choose for this role can host the domain root directory for more than one FedFS domain. It can export other filesystems as well.
Several servers can play host to the same domain root export, as long as there is a mechanism for keeping the content of the domain root export precisely in sync across all the NFS servers (for example, try rsync with the --xattrs option to sync junctions). The DNS SRV format which is used by clients to find FedFS domain root directories can list one or more servers as a FedFS domain's root directory server.
Once you have chosen an NFS server, set it up as a FedFS-enabled NFS server.
Create the domain root export and directories
FedFS-enabled clients use a well-known export pathname when contacting the NFS server that exports a FedFS domain root. That pathname is /.domainroot/fedfs-domain-name .
fedfs-utils 0.10 comes with a tool for managing domain root exports called "fedfs-domainroot."
To add a new domain root directory, become root on the chosen domainroot NFS server and use
# fedfs-domainroot add fedfs-domain-name
This creates the domain root directory on your fileserver and exports it using the proper export pathname. Domain root directories are created in "/.domainroot" on your fileserver.
Read about how to add content to your FedFS domain root directories in Setting up junction resolution support on your Linux NFS Server and Managing junctions with the nfsref command.
The standard export path for FedFS domain root directories is specified in RFC 6641. Preliminary versions of this document specified a different and incompatible export path for domain root directories. If your domain must support legacy FedFS clients (for example, clients still using fedfs-utils-0.8) you may want to provide both types of domain root directories.
See Setting up a FedFS domain root server in the fedfs-utils-0.8 Installation Guide for more details.