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Re: [Xen-devel] xenolinux /dev/random

To: Steve Traugott <stevegt@xxxxxxxxxxxxx>
Subject: Re: [Xen-devel] xenolinux /dev/random
From: Kip Macy <kmacy@xxxxxxxxxxx>
Date: Fri, 14 May 2004 06:57:13 -0700 (PDT)
Cc: Steven Hand <Steven.Hand@xxxxxxxxxxxx>, Ian Pratt <Ian.Pratt@xxxxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxxx, joyce@xxxxxxxxxxxxx, awclarke@xxxxxxxxxxx
Delivery-date: Fri, 14 May 2004 14:58:27 +0100
Envelope-to: Steven.Hand@xxxxxxxxxxxx
In-reply-to: <20040514014250.GA9904@pathfinder>
References: <E1BOAPR-0001Pu-00@xxxxxxxxxxxxxxxxx> <20040513075236.B20816@xxxxxxxxxxxxxxxxxxxxx> <20040514014250.GA9904@pathfinder>
>
> Right now the only reason I'm even using NFS is because a Xenoserver
> provider needs to be able to do backups, migration, failover, and so on.
> How are other people meeting these requirements?  Has the CoW
> development stalled?  What about live migration?

I think iSCSI is the way to go. However, I don't know of any good open
source iSCSI targets.


                                        -Kip

>
> Steve
>
> On Thu, May 13, 2004 at 07:54:57AM -0700, Kip Macy wrote:
> > Are you also using Linux as an NFS server? We use Linux extensively
> > in-house for client machines and have not seen this. Although I'm sure
> > we don't use the default Linux settings.
> >
> >
> >                             -Kip
> >
> >
> > On Thu, 13 May 2004, Steven Hand wrote:
> >
> > >
> > > >My goodness!  See the message I just now posted to xen-devel about NFS
> > > >root hangs; could this be what we're hitting?  The most recent hang we
> > > >saw happened while an rsync was running over ssh *and* someone restarted
> > > >apache...
> > > >
> > > >This wouldn't cause the "NFS server not responding/NFS server OK"
> > > >messages on the domain's console, though (or does that show up as a
> > > >symptom of this too?)
> > >
> > > I don't think this is the cause of the NFS hangs you've been seeing; that
> > > appears to be a generic linux thing (at least we see it with our regular
> > > linux boxes as well as with xen boxes); however if you want to test the
> > > theory the easiest thing to do is to change the /dev/random device node
> > > to be an alias for /dev/urandom (a non-blocking but potentiallyweaker
> > > source of randomness).
> > >
> > > The /dev/random bug only really manifested for us during boot, only on
> > > Xen, and resulted in a permanenent hang.
> > >
> > > The "NFS server foo not responding" followed by later "NFS server foo OK"
> > > messages from linux appear to be due to a combination of stupid timeouts
> > > in the linux sunrpc code and another bug which can cause automounters
> > > to fall into an uninterruptible sleep. If you check "ps auwwx" on a
> > > machine which is having problems and notice proceesses in state 'D'
> > > then this is biting you. Even if this doesn't occur, the crappy timeouts
> > > in the regular linux code mean that linux perfroms very badly if it gets
> > > any errors/loss/congestion during nfs operations.
> > >
> > > cheers,
> > >
> > > S.
> > >
> > >
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> --
> Stephen G. Traugott  (KG6HDQ)
> UNIX/Linux Infrastructure Architect, TerraLuna LLC
> stevegt@xxxxxxxxxxxxx
> http://www.stevegt.com -- http://Infrastructures.Org
>
>
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