source: branches/samba-3.2.x/docs-xml/smbdotconf/locking/fakeoplocks.xml

<samba:parameter name="fake oplocks"
                                 type="boolean"
                 context="S"
                 xmlns:samba="http://www.samba.org/samba/DTD/samba-doc">
<description>
        <para>Oplocks are the way that SMB clients get permission 
        from a server to locally cache file operations. If a server grants 
        an oplock (opportunistic lock) then the client is free to assume 
        that it is the only one accessing the file and it will aggressively 
        cache file data. With some oplock types the client may even cache 
        file open/close operations. This can give enormous performance benefits.
        </para>

        <para>When you set <command moreinfo="none">fake oplocks = yes</command>, <citerefentry>
        <refentrytitle>smbd</refentrytitle><manvolnum>8</manvolnum></citerefentry> will
        always grant oplock requests no matter how many clients are using the file.</para>

        <para>It is generally much better to use the real <smbconfoption name="oplocks"/> support rather 
        than this parameter.</para>
                
        <para>If you enable this option on all read-only shares or 
        shares that you know will only be accessed from one client at a 
        time such as physically read-only media like CDROMs, you will see 
        a big performance improvement on many operations. If you enable 
        this option on shares where multiple clients may be accessing the 
        files read-write at the same time you can get data corruption. Use 
        this option carefully!</para>
</description>
<value type="default">no</value>
</samba:parameter>