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Re: [Xen-users] Live migration and drbd

To: "Nathan Stratton" <nathan@xxxxxxxxxxxx>
Subject: Re: [Xen-users] Live migration and drbd
From: "Andrew Lyon" <andrew.lyon@xxxxxxxxx>
Date: Mon, 10 Nov 2008 20:11:35 +0000
Cc: xen-users@xxxxxxxxxxxxxxxxxxx, danielsaori@xxxxxxxxx
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On Mon, Nov 10, 2008 at 7:48 PM, Nathan Stratton <nathan@xxxxxxxxxxxx> wrote:
> On Mon, 10 Nov 2008, Andrew Lyon wrote:
>>> http://www.asplund.nu/xencluster/xen-cluster-howto.html
>> I plan to try this soon, I've read the guide and it all makes sense to
>> me, but could somebody explain why using drbd on top of lvm is
>> preferable to using drbd with physical devices and lvm on the drbd
>> devices?
> I would also love to know the answer to this, currently I am running;
> Disk > DRBD > LVM2 > GFS > xen tap:aio
> and:
> Disk > DRBD > LVM2 > xen phy:{lvm lv}

What happens if you make a lvm snapshot in that setup (the 2nd)? I
assume lvm on the second node would need to re-read the lvm metadata?
And if you extend the logical volume?

I've spent a lot of time googling this and while I can find plenty of
documentation I am unable to find anything that explains the reasoning
and theory behind it.

> The 2nd is obliviously faster, then the first, but I have not moved
> everything over yet.
> Would moving DRBD on LVM2 make things faster or slower? The downside I can
> see is that you need to build a DRBD config for every domu, what makes this
> overhead worth it?
>> <>
> Nathan Stratton                                CTO, BlinkMind, Inc.
> nathan at robotics.net                         nathan at blinkmind.com
> http://www.robotics.net                        http://www.blinkmind.com

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