Re: [Qemu-devel] "File too large" error from "qemu-img snapshot" (was Re: AW: Bug Repoting Directions Request)

[Kevin Wolf]

Am 22.11.2014 um 18:02 hat Prof. Dr. Michael Schefczyk geschrieben:
> Dear All,
> 
> after some trying, my impression is that the following steps do work with 
> plain Centos 7:
> 
> virsh snapshot-create-as VM backsnap
> qemu-img convert -f qcow2 -s backsnap -O qcow2 VM.img backup.img
> virsh snapshot-delete VM backsnap
> 
> Am I on the right track with these commands?

I won't tell you that you're bound to break your image with this
sequence, because chances are that you won't break it. (In practice,
this happens to work in most cases, because the essential snapshot
metadata generally isn't written to without explicit user actions on
that snapshot.)

But you're violating the rule of "one writer or many readers", so as far
as qemu is concerned, we won't be careful to avoid breaking this setup.
Don't blame us if it fails one day.

With the QMP solutions (either drive-backup or snapshot/commit) you're
using official APIs, so I'd encourage you to use these.

Kevin

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