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Re: [Qemu-devel] [RFC] live snapshot, live merge, live block migration


From: Jagane Sundar
Subject: Re: [Qemu-devel] [RFC] live snapshot, live merge, live block migration
Date: Thu, 12 May 2011 20:16:08 -0700
User-agent: Mozilla/5.0 (Windows; U; Windows NT 6.1; en-US; rv:1.9.2.17) Gecko/20110414 Thunderbird/3.1.10

On 5/12/2011 8:33 AM, Jes Sorensen wrote:
On 05/09/11 15:40, Dor Laor wrote:
Summary:
   * We need Marcelo's new (to come) block copy implementation
     * should work in parallel to migration and hotplug
   * General copy on read is desirable
   * Live snapshot merge to be implemented using block copy
   * Need to utilize a remote block access protocol (iscsi/nbd/other)
     Which one is the best?
   * Keep qemu-img the single interface for dirty block mappings.
   * Live block migration pre copy == live copy + block access protocol
     + live migration
   * Live block migration post copy == live migration + block access
     protocol/copy on read.

Comments?
I think we should add Jagane Sundar's Livebackup to the watch list here.
It looks very interesting as an alternative way to reach some of the
same goals.

Cheers,
Jes
Thanks for the intro, Jes. I am very interested in garnering support for Livebackup.

You are correct in that Livebackup solves some, but not all, problems in the same space.

Some comments about my code: It took me about two months of development before I connected with you on the list. Initially, I started off by doing a dynamic block transfer such that fewer and fewer blocks are dirty till there are no more dirty blocks and we declare the backup complete. The problem with this approach was that there was no real way to plug in a guest file system quiesce function. I then moved on to the snapshot technique. With this snapshot technique I am also able to test the livebackup function very thoroughly - I use a technique where I create a LVM snapshot simultaneously, and do a cmp of the LVM snapshot and the livebackup backup image.

With this mode of testing, I am very confident of the integrity of my solution.

I chose to invent a new protocol that is very simple, and custom to livebackup, because I needed livebackup specific functions such as 'create snapshot', 'delete snapshot', etc. Also, I am currently implementing SSL based encryption with both client authenticating to server and server authenticating to client using self signed certificate.
iSCSI or NBD would be more standards compliant, I suppose.

My high level goal is to make this a natural solution for Infrastructure As A Cloud environments. I am looking carefully at integrating the management of the Livebackup function into Openstack.

I would like to help in any way I can to make KVM be the *best* VM technology for IaaS clouds.

Thanks,
Jagane






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