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<chapter id="msdfs">
<chapterinfo>
<author>
<firstname>Shirish</firstname><surname>Kalele</surname>
<affiliation>
<orgname>Samba Team & Veritas Software</orgname>
<address>
<email>samba@samba.org</email>
</address>
</affiliation>
</author>
&author.jht;
<pubdate>12 Jul 2000</pubdate>
</chapterinfo>
<title>Hosting a Microsoft Distributed File System tree on Samba</title>
<sect1>
<title>Features and Benefits</title>
<para>
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.
</para>
<para>
For information about DFS, refer to the
<ulink url="http://www.microsoft.com/NTServer/nts/downloads/winfeatures/NTSDistrFile/AdminGuide.asp">Microsoft documentation</ulink>.
This document explains how to host a DFS tree on a UNIX machine (for DFS-aware
clients to browse) using Samba.
</para>
<para>
To enable SMB-based DFS for Samba, configure it with the <option>--with-msdfs</option>
option. Once built, a Samba server can be made a DFS server by setting the global
Boolean <smbconfoption><name>host msdfs</name></smbconfoption>
parameter in the &smb.conf; file. You designate a share as a DFS
root using the Share Level Boolean <smbconfoption><name>msdfs root</name></smbconfoption> 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
<filename>junction->msdfs:storage1\share1</filename> 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, <parameter>\\storage1\share1</parameter>).
</para>
<para>
DFS trees on Samba work with all DFS-aware clients ranging from Windows 95 to 200x.
<link linkend="dfscfg"/> shows how to setup a DFS tree on a Samba server.
In the <filename>/export/dfsroot</filename> directory, you set up your DFS links to
other servers on the network.
<screen>
&rootprompt;<userinput>cd /export/dfsroot</userinput>
&rootprompt;<userinput>chown root /export/dfsroot</userinput>
&rootprompt;<userinput>chmod 755 /export/dfsroot</userinput>
&rootprompt;<userinput>ln -s msdfs:storageA\\shareA linka</userinput>
&rootprompt;<userinput>ln -s msdfs:serverB\\share,serverC\\share linkb</userinput>
</screen>
</para>
<para>
<smbconfexample id="dfscfg">
<title>smb.conf with DFS configured</title>
<smbconfsection>[global]</smbconfsection>
<smbconfoption><name>netbios name</name><value>&example.server.samba;</value></smbconfoption>
<smbconfoption><name>host msdfs </name><value>yes</value></smbconfoption>
<smbconfsection>[dfs]</smbconfsection>
<smbconfoption><name>path</name><value>/export/dfsroot</value></smbconfoption>
<smbconfoption><name>msdfs root</name><value>yes</value></smbconfoption>
</smbconfexample>
</para>
<para>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.</para>
<para>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.</para>
</sect1>
<sect1>
<title>Common Errors</title>
<itemizedlist>
<listitem><para>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.</para>
</listitem>
<listitem><para>Currently, there's a restriction that msdfs
symlink names should all be lowercase.</para>
</listitem>
<listitem><para>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.</para>
</listitem>
</itemizedlist>
<sect2>
<title>MSDFS UNIX Path Is Case-Critical</title>
<para>
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.
</para>
<para><quote>
I spent some time trying to figure out why my particular
dfs root wasn't working. I noted in the documenation 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.
</quote></para>
<para>
For example, I had a share defined as such:
<screen>
[pub]
path = /export/home/Shares/public_share
msdfs root = yes
</screen>
and I could not make my Windows 9x/Me (with the dfs client installed)
follow this symlink:
<screen>
damage1 -> msdfs:damage\test-share
</screen>
</para>
<para>
Running a debug level of 10 reveals:
<programlisting>
[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.
</programlisting>
Curious. So I changed the directory name from .../Shares/... to
.../shares/... (along with my service definition) and it worked!
</para>
</sect2>
</sect1>
</chapter>
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