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Re: [Qemu-devel] Can qemu reopen image files?
From: |
Eric Blake |
Subject: |
Re: [Qemu-devel] Can qemu reopen image files? |
Date: |
Thu, 29 Dec 2016 07:42:28 -0600 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.5.1 |
On 12/28/2016 12:51 PM, Christopher Pereira wrote:
> Hi Eric,
>
> There is something I don't understand.
>
> We are doing: "virsh save", "qemu-img convert", "qemu-img rebase" and
> "virsh restore".
> We only touch the backing chain by doing the rebase while the VM is down.
> Is there any chance this procedure can destroy data?
Since there are never two active writers to the file (you have made sure
that qemu-img and qemu are not both holding the same file open at once),
there is no chance for corruption on that front. There's still a
possibility of corruption if you botch the instructions, and don't
rebuild the chain in such a way that the guest would see the same data,
but that's harder to say without seeing an actual transcript.
> If so, is there any difference between shutting down and just
> saving/restoring the VM?
Shutting down vs. saving/restoring shouldn't matter other than the
length of time that the guest is offline (including rebooting time with
a shut down, which is not present for an incoming migration restoration).
> Maybe save/restore keeps a cache?
No. Both shutting down and saving end the qemu process, and therefore
flush everything to the disk.
--
Eric Blake eblake redhat com +1-919-301-3266
Libvirt virtualization library http://libvirt.org
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- [Qemu-devel] Can qemu reopen image files?, Christopher Pereira, 2016/12/18
- Re: [Qemu-devel] Can qemu reopen image files?, Fam Zheng, 2016/12/18
- Re: [Qemu-devel] Can qemu reopen image files?, Stefan Hajnoczi, 2016/12/19
- Re: [Qemu-devel] Can qemu reopen image files?, Christopher Pereira, 2016/12/19
- Re: [Qemu-devel] Can qemu reopen image files?, Eric Blake, 2016/12/19
- Re: [Qemu-devel] Can qemu reopen image files?, Christopher Pereira, 2016/12/19
- Re: [Qemu-devel] Can qemu reopen image files?, Christopher Pereira, 2016/12/28
- Re: [Qemu-devel] Can qemu reopen image files?,
Eric Blake <=
- Re: [Qemu-devel] Can qemu reopen image files?, Eric Blake, 2016/12/29
- Re: [Qemu-devel] Can qemu reopen image files?, Eric Blake, 2016/12/29
- Re: [Qemu-devel] Can qemu reopen image files?, Eric Blake, 2016/12/29