Hosting a Microsoft Distributed File System tree on Samba

Instructions

The Distributed File System (or Dfs) provides a means of - separating the logical view of files and directories that users - see from the actual physical locations of these resources on the - network. It allows for higher availability, smoother storage expansion, - load balancing etc. For more information about Dfs, refer to Microsoft documentation.

This document explains how to host a Dfs tree on a Unix - machine (for Dfs-aware clients to browse) using Samba.

To enable SMB-based DFS for Samba, configure it with the - --with-msdfs option. Once built, a - Samba server can be made a Dfs server by setting the global - boolean host msdfs parameter in the smb.conf - file. You designate a share as a Dfs root using the share - level boolean msdfs root parameter. A Dfs root directory on - Samba hosts Dfs links in the form of symbolic links that point - to other servers. For example, a symbolic link - junction->msdfs:storage1\share1 in - the share directory acts as the Dfs junction. When Dfs-aware - clients attempt to access the junction link, they are redirected - to the storage location (in this case, \\storage1\share1).

Dfs trees on Samba work with all Dfs-aware clients ranging - from Windows 95 to 2000.

Here's an example of setting up a Dfs tree on a Samba - server.

# The smb.conf file:
-[global]
-	netbios name = SAMBA
-	host msdfs   = yes
-
-[dfs]
-	path = /export/dfsroot
-	msdfs root = yes
-

In the /export/dfsroot directory we set up our dfs links to - other servers on the network.

root# cd /export/dfsroot

root# chown root /export/dfsroot

root# chmod 755 /export/dfsroot

root# ln -s msdfs:storageA\\shareA linka

root# ln -s msdfs:serverB\\share,serverC\\share linkb

You should set up the permissions and ownership of - the directory acting as the Dfs root such that only designated - users can create, delete or modify the msdfs links. Also note - that symlink names should be all lowercase. This limitation exists - to have Samba avoid trying all the case combinations to get at - the link name. Finally set up the symbolic links to point to the - network shares you want, and start Samba.

Users on Dfs-aware clients can now browse the Dfs tree - on the Samba server at \\samba\dfs. Accessing - links linka or linkb (which appear as directories to the client) - takes users directly to the appropriate shares on the network.

Notes

Windows clients need to be rebooted - if a previously mounted non-dfs share is made a dfs - root or vice versa. A better way is to introduce a - new share and make it the dfs root.
Currently there's a restriction that msdfs - symlink names should all be lowercase.
For security purposes, the directory - acting as the root of the Dfs tree should have ownership - and permissions set so that only designated users can - modify the symbolic links in the directory.