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

[Jagane Sundar <jagane@sundar.org>]

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