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The Distributed File System (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, and so on.
For information about DFS, refer to the Microsoft documentation. This document explains how to host a DFS tree on a UNIX machine (for DFS-aware clients to browse) using Samba.
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 200x.
Following sample configuration shows how to setup a DFS tree on a Samba server.
In the /export/dfsroot directory, you set up your DFS links to
other servers on the network.
root#cd /export/dfsrootroot#chown root /export/dfsrootroot#chmod 755 /export/dfsrootroot#ln -s msdfs:storageA\\shareA linkaroot#ln -s msdfs:serverB\\share,serverC\\share linkb
Example 19.1. smb.conf with DFS configured
[global] |
netbios name = GANDALF |
host msdfs = yes |
[dfs] |
path = /export/dfsroot |
msdfs root = yes |
You should set up the permissions and ownership of the directory acting as the DFS root so 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.
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 only designated users can modify the symbolic links in the directory.
A network administrator sent advice to the Samba mailing list after a long sessions trying to determine why DFS was not working. His advice is worth noting.
“ I spent some time trying to figure out why my particular dfs root wasn't working. I noted in the documentation that the symlink should be in all lowercase. It should be amended that the entire path to the symlink should all be in lowercase as well. ”
For example, I had a share defined as such:
[pub] path = /export/home/Shares/public_share msdfs root = yes
and I could not make my Windows 9x/Me (with the dfs client installed) follow this symlink:
damage1 -> msdfs:damage\test-share
Running a debug level of 10 reveals:
[2003/08/20 11:40:33, 5] msdfs/msdfs.c:is_msdfs_link(176) is_msdfs_link: /export/home/shares/public_share/* does not exist.
Curious. So I changed the directory name from .../Shares/... to .../shares/... (along with my service definition) and it worked!