libvirt users - Apr 2014 - Re: Live snapshot merging (qemu 2.0)

Hello.

The Changelog of qemu-2.0.0 mentioned "Live snapshot merging". Someone
has an idea what could be ment by this? I'm asking because i'm still
struggling with finding a reliable backup solution for running kvm
machines. Blockcopy is my current solution.

best regards
Thomas

On 04/22/2014 01:47 AM, Thomas Stein wrote:
> Hello.
> 
> The Changelog of qemu-2.0.0 mentioned "Live snapshot merging".
Someone
> has an idea what could be ment by this? I'm asking because i'm
still
> struggling with finding a reliable backup solution for running kvm
> machines. Blockcopy is my current solution.
"Live snapshot merging" means going from a backing chain of "base
<-
img" to "base" by merging the contents of img into base.  Libvirt
does
not yet support this action, but we are getting closer with our work on
tracking the entire backing chain in domain XML.

Current libvirt is able to support some chain shortening operations with
older qemu: libvirt can do snapshot merging of any backing file (taking
"base <- snap1 <- snap2" to "base <- snap2" by
committing snap1 into
base), as well as pulling content into the active layer (going from
"base <- snap1 <- snap2" to "base <- snap2" by
pulling snap1 into
snap2).  And as you mentioned, using blockcopy also allows libvirt to
pivot to a new shorter backing chain.

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

Am 22.04.14 14:00, schrieb Eric Blake:
> On 04/22/2014 01:47 AM, Thomas Stein wrote:
>> Hello.
>> 
>> The Changelog of qemu-2.0.0 mentioned "Live snapshot
merging". Someone
>> has an idea what could be ment by this? I'm asking because i'm
still
>> struggling with finding a reliable backup solution for running kvm
>> machines. Blockcopy is my current solution.
> 
> "Live snapshot merging" means going from a backing chain of
"base <-
> img" to "base" by merging the contents of img into base. 
Libvirt does
> not yet support this action, but we are getting closer with our work on
> tracking the entire backing chain in domain XML.
> 
> Current libvirt is able to support some chain shortening operations with
> older qemu: libvirt can do snapshot merging of any backing file (taking
> "base <- snap1 <- snap2" to "base <- snap2" by
committing snap1 into
> base), as well as pulling content into the active layer (going from
> "base <- snap1 <- snap2" to "base <- snap2" by
pulling snap1 into
> snap2).  And as you mentioned, using blockcopy also allows libvirt to
> pivot to a new shorter backing chain.
Thanks Eric for the explanation.

cheers
t.