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Downtime of any instance during live-migration

asked 2015-04-14 05:15:02 -0500

BhavaniPrasad gravatar image

I have done the Multi compute node shared storage setup for testing live migration, able to migrate the instance from one compute to another compute but i could see downtime of instance during migration.

I observe 24% of packet loss during migration and i followed below link to configure my setup.

Is it exepected behaviour or am i missing something in configuration to acheive zero down time?

I was trying this on KVM hypervisor.

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answered 2015-04-15 02:31:15 -0500

Ranjit gravatar image

you can visit having performance analysis (migration time and downtime).

From my understanding , there will be downtime but the downtime depends the state of VM memory.

hypervisors are using either of the two technique to do the memory state transfer from one host to another host. Pre-copy memory migration or Post-copy memory migration.

Visit wiki link to know more.

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Thanks for your quick reply!! I have gone through your blog. It was nice. I got that there will be a downtime for instance during live migration.

BhavaniPrasad gravatar imageBhavaniPrasad ( 2015-04-15 08:24:26 -0500 )edit

answered 2015-05-12 09:58:45 -0500

amic gravatar image

The downtime of a VM during its live migration is given mostly by the VM RAM activity (change rate). Qemu itself allows to setup the value of the maximum amount you are willing to "sacrifice" as a downtime. Unfortunately this value is not in Openstack. The downtime window is provided to transfer the last chunk of dirtied memory (and CPU states) and directly affects convergency of the pre-copy algorithm. Could you please be more specific about your use case? What kind of VM are you trying to migrate? What kind of load does it carry on? What is the downtime value in time unit (How many packets got lost and what is the interval between following two). How long does it take to migrate the VM, version of Qemu/libvirt, etc, ... Assuming you are trying to live migrate essentially unloaded VM, from my experience the downtime doesn't exceed 1s..

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Asked: 2015-04-14 05:15:02 -0500

Seen: 330 times

Last updated: May 12 '15