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Re: [Xen-users] Live migration-delay in gratuitous arp

To: xen-users@xxxxxxxxxxxxxxxxxxx
Subject: Re: [Xen-users] Live migration-delay in gratuitous arp
From: Jamon Camisso <jamonation@xxxxxxxxx>
Date: Wed, 12 Jan 2011 03:04:01 -0500
Delivery-date: Tue, 11 Jan 2011 19:05:24 -0800
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On 1/11/2011 9:51 PM, Virajith Jalaparti wrote:

I was trying to perform live migration with a VM on a LAN and measure
the downtime seen by an application (e.g. ping), the time for which the
application cannot communicate with the VM. The application is run on a
machine different from those between which the VM is migrated. I noticed
that the VM remains unreachable for nearly 1-1.5sec. However the
xend.log file says that the time (the delta) for the last round of the
migration is around 100msec. So, the VM is actually paused for just
around 100msec but the application cannot reach it for 1-1.5sec. I
believe this is because of the delay in the gratuitous ARP being sent.
Is the implementation such that the ARP is not sent immediately after
the migration is finished? Is there an easy tweak (without modifying
source code) by which I can correct this or do I have to modify the
source code?

I am using Xen from the repos of CentOS 5.5 on a 64bit machine.

I'd be interested to hear if running arping in screen during migration on your domU has any effect.


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