make the experimental NFS subsystem the default one

[Bob Friesenhahn]

On Wed, 27 Apr 2011, Rick Macklem wrote:
>
> I don't know anything about ZFS, but I would think that, if you see a
> major performance improvement, that ZFS isn't committing stuff to logs
> so that data won't be lost.
>
> Maybe the ZFS folks can comment? (I don't remember seeing the details
> of what you change? If you sent a patch, sorry, but I've misplaced it.)

Zfs will loose as much as 5 seconds worth of data (and maybe even 10 
seconds) if the data is written slowly and/or the server has quite a 
lot of RAM.  It commits data in order so the written data will be 
completely coherent for that snapshot in time, but the result may 
still be completely corrupted from the client's perspective.  5 (or 
10!) seconds of data could be quite a lot of data, and could represent 
entire new directory trees, or large directory trees which were 
removed.  Individual file content could be overwritten hundreds of 
times before the point where the server arbitrarily decides to commit 
it.

If the server bounces, its data won't match what the client thinks it 
should have.

Bob
-- 
Bob Friesenhahn
bfriesen at simple.dallas.tx.us, http://www.simplesystems.org/users/bfriesen/
GraphicsMagick Maintainer,    http://www.GraphicsMagick.org/