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Date:      Fri, 02 Mar 2007 08:56:04 -0600
From:      Eric Anderson <anderson@freebsd.org>
To:        Steven Hartland <killing@multiplay.co.uk>
Cc:        freebsd-hackers@freebsd.org, freebsd-stable@freebsd.org
Subject:   Re: sysinstall creates corrupt filesystems after repartitioning
Message-ID:  <45E83B04.2010009@freebsd.org>
In-Reply-To: <00ac01c75cd8$4e5d57e0$b3db87d4@multiplay.co.uk>
References:  <00cb01c75c5b$4205e390$b3db87d4@multiplay.co.uk> <45E82660.4030107@freebsd.org> <008101c75cd1$42a4df10$b3db87d4@multiplay.co.uk> <45E830A8.8020104@freebsd.org> <00ac01c75cd8$4e5d57e0$b3db87d4@multiplay.co.uk>

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On 03/02/07 08:37, Steven Hartland wrote:
> Eric Anderson wrote:
>> On 03/02/07 07:46, Steven Hartland wrote:
>> Mounting an NFS share on top of a skimmed down /usr is very common,
>> and very desirable.  You may mount /usr from a small read-only
>> partition (vnode file, etc) and then mount a different partition or
>> NFS over it if you detect the one you want.
>>
>> I think this comes down to: if it hurts, stop doing it.  :)
>>
>> Maybe sysinstall should warn you that you are double mounting, but I
>> don't want it to stop letting me do it.
> 
> Interesting if that's a valid thing to do why does everything
> break when its done? Is it ment to be doing a union hence you get
> the combined contents of both? If so its not working correctly in
> this case :( Can you provide me with more info on how this is
> supposed to work eric please.


No, it won't do a union unless you use union.  Things break because you 
mounted an empty /usr on top of a working /usr.  That just breaks 
things, because you probably need binaries in /usr.

The OS doesn't know whether you want to mount an empty fs on a populated 
one, or what.  It does exactly what you ask it to do, and in this case, 
it was a bad thing.

Think of a thin client that has just enough stuff in /usr to make it 
boot and run a few tools.  Then, depending on a startup option, it 
mounts a more populated /usr from NFS (or even a local disk, doesn't 
really matter) over the previous /usr.

The fact is this:  you made a new partition, called it /usr, and told 
sysinstall to mount it.  It did.  That happened to be a problem for you, 
which I could imagine it would be.   Now, I'm not claiming this is the 
cause of your file system corruption issues.  I'm just saying the 
duplicate mount is not a bug, it's a feature.

Eric





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