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Date:      Sat, 27 Apr 2002 15:27:18 +0100
From:      Brian Candler <B.Candler@pobox.com>
To:        "Andrew P. Lentvorski" <bsder@allcaps.org>
Cc:        freebsd-fs@freebsd.org, freebsd-net@freebsd.org
Subject:   Re: NFS clearing attribute cache in nfs_open
Message-ID:  <20020427152718.A16634@linnet.org>
In-Reply-To: <20020426162442.N8693-100000@mail.allcaps.org>
References:  <20020426181535.B2748@linnet.org> <20020426162442.N8693-100000@mail.allcaps.org>

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On Fri, Apr 26, 2002 at 04:42:48PM -0700, Andrew P. Lentvorski wrote:
> > ... Could it safely be made less restrictive, e.g. don't
> > clear the cache when opening a file for read?
> 
> In a word, no.  Why couldn't the sysadmin be running "make installworld"
> on the NFS server while you're running that program?  By definition, for
> better or worse, NFS is "stateless".  The only way in which NFS can know
> that your file hasn't changed (been deleted, renamed, etc) is to make that
> round trip to the server.  Sorry.

Sounds fair. I was talking about the _attribute_ cache, but does re-fetching
the attributes also tell the client that the _content_ of a file has
changed? A version number, perhaps?

> If you are really
> into clusters with low-latency, you might want to look into something like
> NFS V4 (Is anybody working on that on FreeBSD, anymore?), AFS, CODA, or
> something more specialized.  Those networked filesystems have a
> bidrectional characteristic and cached state protocols so that they can
> minimize communication.

Will do. For a diskless bootup I think I am restricted to either NFS or
ramdisk for the root filesystem though.

Is it possible to replace the root filesystem with a different one after the
system has started?

Regards,

Brian.

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