Re: [Qemu-devel] qcow2 - safe on kill? safe on power fail?

[Avi Kivity]

Jamie Lokier wrote:
> > It's a simple matter of allocating, making sure the allocation is on 
> > disk, and recording that allocation in the tables.
> >     
>
> The simple implementations are only safe if sector writes are atomic.
>
> Opinions from Google seem divided about when you can assume that,
> especially when the underlying file or device is not directly mapped
> to disk sectors.
>   

That's worrying.  I guess always-allocate-on-write solves that (with 
versioned roots in well-known places), but that's not qcow2 any more -- 
it's btrfs.  And given that btrfs ought to allow file-level snapshots, 
perhaps the direction should be raw files on top of btrfs (which could 
be extended to do block sharing, yay!)

--
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.