Re: [Qemu-devel] [RFC] qed: Add QEMU Enhanced Disk format

[Kevin Wolf]

Am 10.09.2010 13:43, schrieb Stefan Hajnoczi:
>>>>> By creating two code paths within qcow2.
>>>>
>>>> You're creating two code paths for users.
>>>
>>> No, I'm creating a single path: QED.
>>>
>>> There are already two code paths: raw and qcow2.  qcow2 has had such a bad
>>> history that for a lot of users, it's not even a choice.
>>
>> qcow2 exists, people use it, and by the time qed is offered on distros (even
>> more on enterprise distros), there will be a lot more qcow2 images.  Not
>> everyone runs qemu.git HEAD.
>>
>> What will you tell those people?  Upgrade your image?  They may still want
>> to share it with older installations.  What if they use features not present
>> in qed?  Bad luck?
>>
>> qcow2 is going to live forever no matter what we do.
> 
> It should be possible to do (live) upgrades for supported images.

That still leaves those qcow2 images that use features not supported by
qed. Just a few features missing in qed are internal snapshots, qcow2 on
block devices, compression, encryption. So qed can't be a complete
replacement for qcow2 (and that was the whole point of doing qed). If
anything, it can exist besides qcow2.

Kevin