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Date:      Wed, 4 Mar 1998 10:34:04 -0500 (EST)
From:      "Ron G. Minnich" <rminnich@Sarnoff.COM>
To:        Niall Smart <njs3@doc.ic.ac.uk>
Cc:        Tom <tom@sdf.com>, "Ron G. Minnich" <Sarnoff.COM!rminnich@minas-tirith.pol.ru>, Alex Povolotsky <tarkhil@minas-tirith.pol.ru>, hackers@FreeBSD.ORG
Subject:   Re: Cluster?
Message-ID:  <Pine.SUN.3.91.980304102946.27680D-100000@terra>
In-Reply-To: <E0yACqr-0005la-00@oak2.doc.ic.ac.uk>

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> On Mar 3, 11:04pm, Tom wrote:
> I think a good approach to transparent clustering is through distributed
> shared memory.  However, the coherencey schemes used for high reliability

yes, this has been an active area too. DSM is great, we build 'em, we use
'em, but it's not the panacea. It's just good for some things, poor for
others. 

> I'd be more than interested in adding some DSM support to FreeBSD
> to support transparent fall-over clustering.  

well, it's a nice goal, the trick is getting the VM fixed, and other
pieces fixed, so that it will work. I tried to get this to happen in 1994,
when I offered FreeBSD MNFS (see web page for info on MNFS), but the
reception was muted, although some projects in some places did use MNFS. 

Note that Chuck Cranor's UVM fixes the problems, but it is only in 
OpenBSD and NetBSD. ah well. 

In terms of crash resilience: while not perfect, MNFS was as crash
resilient as NFS, and in fact we used it to support DSM for migrating
Condor processes. Condor processes migrate by sending themselves a signal
and dumping core, and then restarting the corefile elsewhere. 

ron


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