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Re: [libvirt] suggestions on snapshotting testing



On 05/21/2012 10:54 PM, Eric Blake wrote:
> 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.

Yeah I already have a local copy. Will post when I have detail. Thank you.

> 
>>>
>>> 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).

Yeah, I'm leaning towards on-line disk snapshots. (as I don't care much about VM state at
the moment).

Thanks again for the detail
> 
>>
>>>
>>> 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.
>>
>>
> 


-- 
/kashyap


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