You shouldn't put an NFS mount point in a directory with ANY other
stuff.  If you do, then when an NFS server dies, painful things will
happen.  Since root always has other stuff in it, you should never put
NFS mount points there.

Here are the painful things:

    (1) Accessing the directory with the busted mount will hang.
        
        (If you are lucky, then the thing you are looking up will
        be before the busted mount, and you won't hang.  Murphy says
        it will be after the busted mount, and so it will hang.)

    (2) Doing a "pwd" in any descendant of the directory may hang.

        This is actually just a special case of the first problem.  
        In order to figure out where you are, the "pwd" command
        reads all the directories above the current one.  If it
        hits a directory with a busted mount point, it will hang.

So a bad mount point scheme would be:

        /nfs/FOO                - mount point for root of server FOO
        /nfs/BAR                - mount point for root of server BAR

If server FOO dies, then you may not be able to get to /nfs/BAR.  And
any "pwd" from down inside /nfs/BAR will hang.  In this example,
/nfs/BAR is another NFS mount point, but the same bad things would
happen even if were on local disk.

A good mount point scheme would be:

        /nfs/FOO/root           - mount point for root of server FOO
        /nfs/BAR/root           - mount point for root of server BAR

The general rule is:

    Put all the NFS mounts for a particular server in a directory by
    themselves.  (It's okay to put multiple mounts for the same server
    into a single directory, because if one mount point fails they
    probably all will.)

Dave Hitz               hitz@netapp.com
Network Appliance       (415) 428-5106

WHY?
Why does mounting an NFS filesystem onto the root directory cause problems?

It has to do with the get [c]wd[3C] call, which is actually used rather more
often than you might at first imagine.

It works by stat'ing '.', and then searching for '.' in '..' by stat'ing all
the files in '..' to see which is '.' and hence fined out what the real name
of '.' is.  This procedure is repeated in each successive parent directory 
all the way up to root.  If you stat an NFS mount point, this causes an 
interaction with the NFS server, which at best introduces a delay, and at
worst hangs if the server is not responding.  If you have any mount points
in /, then all get [c]wd(3C) calls will hit them.  Therefore, it is a good
idea to keep NFS mount points out of any directory which is part of anyone's
current working director, and as root is part of everyone's current working
directory, keep them out of that in particular.

Symbolic links from root to an NFS mount point are OKAY.