samba-mirror/docs/howto/msdfs.xml

<chapter id="msdfs">

<chapterinfo>
	<author>
		<firstname>Shirish</firstname><surname>Kalele</surname>
		<affiliation>
			<orgname>Samba Team &amp; 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</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-&gt;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">Following sample configuration</link> 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 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.
		</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>