Buyer Beware: A Major Change in NFS (in Rawhide) is about to happen

[Ric Wheeler]

On 10/27/2009 10:00 AM, James Laska wrote:
> On Mon, 2009-10-26 at 10:34 -0400, Steve Dickson wrote:
>> [With the next nfs-utils rawhide build, I will be flipping the ]
>> [switch that will cause all NFS client mounts to try NFS v4 first ]
>> [At the bottom of this email has the workarounds if this change does ]
>> [indeed cause pain ]
>>
>> As part of the https://fedoraproject.org/wiki/Features/NFSv4Default feature
>> I am one commit away from changing the default protocol version NFS will
>> be using (or at least trying to use).
>>
>> What does this means to you? Hopefully nothing! In theory this should
>> be a very seamless transition but with all new technology there
>> will be (and are) some rough spots.
>>
>> Why are make the change? See the NFSv4Default wiki for details,
>> but in a nutshell:
>>      * Better performance - V4 is now a stateful protocol. Meaning the server keeps
>>        state on all the clients access a particular file or directory. This
>>        allows the server to give out delegations (or leases) which in turn
>>        allows the client to aggressive cache both data and meta data locally
>>
>>      * Firewall Friendly- With v4 only one port is used 2049 for all traffic
>>        including mounting and file locking.
>>
>>      * Finally it enables us use upcoming minor releases of the the protocol.
>>        NFS version 4.1 and pNFS are two example of upcoming minor releases.
>>
>>
>> FYI, V4 was introduced in Fedora Core 2 so it has been around for a while. I
>> personally have been using it for my home directory for a couple years now..
>> For more of the nitty gritty details see
>>      http://www.iaps.com/NFSv4-new-features.html
>>
>> That's the good news... Here is the bad....
>>
>> Because the mount command will try NFS v4 first, mounts to older Linux servers
>> will start failing like:
>>
>>   # mount linux-server:/export /mnt
>>   mount.nfs: mounting linux-server:/export failed, reason given by server:
>>      No such file or directory
>>
>> This is due to a defect in the Linux server exporting code, which is fixed
>> in F-12, *but* there are a number of workarounds
>>
>> On the server (Which is suggested):
>>     * Add the following entry to the /etc/exports file:
>>       / *(ro,fsid=0) Note: 'fsid=0' is explained in the exports(5) man pages.
>>
>> On the client, go back to v3 mounts by doing one of the following:
>>
>>     * Add -o v3 to command line, similar to:
>>          mount linux-server:/export /mnt
>>
>>     * Change the default mount version in the new /etc/nfsmount.conf file by
>>       uncommenting the Nfsvers=3 setting in the 'NFSMount_Global_Options' section.
>>       See nfsmount.conf(5) man page for details. The diff would look like:
>>
>>      --- /etc/nfsmount.conf.orig	2009-10-26 09:30:21.000000000 -0400
>>      +++ /etc/nfsmount.conf	2009-10-26 10:31:30.227443686 -0400
>>      @@ -31,7 +31,7 @@
>>      # Protocol Version [2,3,4]
>>      # This defines the default protocol version which will
>>      # be used to start the negotiation with the server.
>>     -# Defaultvers=4
>>     +Defaultvers=3
>>      #
>>      # Setting this option makes it mandatory the server supports the
>>      # given version. The mount will fail if the given version is
>
> Haven't gone through the full thread yet, but is it worth adding a
> note/admonition to our NFS installation instructions that changing the
> nfs server configuration may be necessary?
>
> http://docs.fedoraproject.org/install-guide/f12/en-US/html/ch03s05s02.html
>
> Thanks,
> James
>


I think that adding a note to the documentation would be a very good thing...

ric