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Re: [Xen-users] Re: cLVM on Debian/Lenny

To: John Madden <jmadden@xxxxxxxxxxx>
Subject: Re: [Xen-users] Re: cLVM on Debian/Lenny
From: Javier Guerra <javier@xxxxxxxxxxx>
Date: Mon, 20 Apr 2009 14:29:42 -0500
Cc: Jan Kalcic <jandot@xxxxxxxxxxxxxx>, Olivier Le Cam <Olivier.LeCam@xxxxxxxxxxxxxxxxxxxxx>, Ferenc Wagner <wferi@xxxxxxx>, xen-users@xxxxxxxxxxxxxxxxxxx, Thiago Camargo Martins Cordeiro <thiagocmartinsc@xxxxxxxxx>
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John Madden wrote:
> > Jan Kalcic wrote:> Now I think I can figure out that there is no difference 
> > between a domU
> > > based on a file block device on top of a cluster file system, let's
> > > suppose OCFS2, and a domU based on physical block device on top of LVM
> > > (cLVM). In both case, I am eventually able to run the domU on both nodes
> > > having data corruption. Neither OCFS2 nor cLVM with their different lock
> > > managers can provide that mechanism to assure consistency. Right? If
> > > yes, I would say that the best solution should always be using LVM, at
> > > least it provides more features.
> Wrong -- sort of.  OCFS2, GFS, Lustre, etc., are CLUSTER filesystems,
> this "clash" you're talking about is actually supposed to be happening.
> And it isn't a "clash," it allows multiple writers.  With a cluster
> filesystem, you should, for example, be able to have two domU's on
> different dom0's writing to the same tap:aio file-based filesystem
> residing on OCFS2.

yes, multiple nodes can use the same (cluster) filesystem; but if you store 
file-based DomUs on that filesystem, you could start the same DomU on two 
nodes, with the same nefarious results.  that's the non-protection he's talking 


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