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



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


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