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Re: [libvirt] suggestions on snapshotting testing



On 05/21/2012 02:59 AM, Kashyap Chamarthy wrote:

>>> http://libvirt.org/formatsnapshot.html
>>
>> That page is live based on libvirt.git, and should be up-to-date with
>> the current implementation; although I would welcome improvements for
>> additional things to mention.
> 
> I'd probably like to add some examples there for each different variant of snapshots just
> to give a practical idea for people referring that page. I'll try to do this over the weekend.
> 
> You mentioned this page is live based on libvirt.git. Can I manually edit the examples
> section?  Just ensuring I'm not messing up around.

The web page only updates when we push your changes to the upstream
libvirt.git.  You can play with your local copy of libvirt.git to your
heart's content (and run 'make' then browse the local contents using a
file:/// URL) all before posting your patch for review here, without
worrying about what will happen to the upstream documentation.  Part of
the review process is making sure that your proposed html changes will
make sense when they go live.

>>
>> Do you have specific scenarios in mind?  Propose a problem that you
>> think a snapshot would help, then ask questions on which APIs you would
>> use to solve that problem.
> 
> Nothing specific in mind. Let me see if I can provide a bit more info.
> I'm testing snapshots in the context of working with FreeIPA project, where I have a test
> set-up w/ multiple guests, with subtle env. changes in them, interacting w/ each other. I
> need keep track of a clean state, a state with a particular env set-up, revert to a
> certain state, etc, often ending up with a tree of (internal)snapshots for each guest.
> 
> I'm just exploring what kind of snapshots are most efficient for these scenarios.

offline system checkpoint snapshots (which is basically a form of
internal disk snapshots) and online disk snapshots (external disk
snapshots, no VM state) are the fastest to create; but it is easier to
boot an offline system checkpoint (the disks are assumed to be in a
stable state when the guest goes offline) compared to a disk snapshot
(if you don't have a guest agent running to quiesce the guest I/O before
taking the snapshot, then the resulting snapshot may require an fsck to
be usable in the context of booting from that snapshot).

> 
>>
>> Do you understand the difference between the various snapshot flavors?
>> There's several orthogonal issues to be aware of, although not all
>> combinations are supported.
> 
> I think I do understand to a certain extent. I previously had a discussion with you when I
> initially started off and captured the notes as a blog post --
> http://kashyapc.wordpress.com/2011/10/04/snapshotting-with-libvirt-for-qcow2-images/
> 
> However, thanks for the nice summary below.
> 

>>
> 
> I'll post more when I have a bit more clarity and more specifics on what I'd like to try.
> 
> I'm a little hazy with the external snapshots as the combinations/tree of snapshots can
> get a bit complex . Though I do use the basic operation in my daily work flow, like:
> 
> =====================
> root ~$ virsh list
>  Id    Name                           State
> ----------------------------------------------------
>  11    f17test                        running
> 
> root ~$
> =====================
> root ~$ virsh domblklist f17test --details
> Type       Device     Target     Source
> ------------------------------------------------
> file       disk       vda        /var/lib/libvirt/images/f17test.qcow2
> 
> root ~$
> =====================
> root ~$ virsh snapshot-create-as f17test cleanf17 cleanf17-box --diskspec
> vda,file=/var/lib/libvirt/images/snap-f17test.qcow2 --disk-only
> Domain snapshot cleanf17 created
> root ~$
> =====================
> root ~$ virsh snapshot-list f17test
>  Name                 Creation Time             State
> ------------------------------------------------------------
>  cleanf17             2012-05-14 00:02:54 +0530 disk-snapshot
> 
> root ~$
> =====================
> 
> Thanks for your response.
> 
> 

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

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