Re: [Qemu-devel] could i using qemu-img covert && rebase -u to do qcow2 rollback?

[Eric Blake]

On 01/04/2016 10:45 AM, Max Reitz wrote:
> On 30.12.2015 12:31, Huan Zhang wrote:
>> Hi,
>> We are finding a way to do rollback for qcow2 in production environment,
>> But we can't ensure the below way will work well, and user data are safe.
>>
>> for example,
>> snap0.qcow2 -> snap1.qcow2 ->snap2.qcow2 -> active.qcow2
>>
>> rollback to snap1 using convert && rebase -u:
>> 1. qemu-img convert -O qcow2 snap1.qcow2 rollback.qcow2
>> 2. qemu-img rebase -u -b snap2.qcow2 rollback.qcow2
> 
> What do you mean by "rollback"? Just getting back to the state presented
> in snap1, discarding all the changes done in snap2 and active?
> 
> Then why don't you just throw snap2.qcow2 and active.qcow2 away and
> continue to work on snap1.qcow2? If you want to keep snap1 in its
> current state, just create a new image on top of it:
> 
> $ qemu-img create -f qcow2 -b snap1.qcow2 active.qcow2

Don't forget to also set the backing format (either '-o
backing_fmt=qcow2' or the undocumented '-F qcow2').  Without an explicit
format, libvirt will default to refusing to honor your backing files
rather than risk an unsafe format probe.

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

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