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Re: [Qemu-devel] using "qemu-img convert -O qcow2" to convert qcow v1 to

From: John Snow
Subject: Re: [Qemu-devel] using "qemu-img convert -O qcow2" to convert qcow v1 to v2 creates a qcow v3 file?
Date: Tue, 14 Nov 2017 15:38:05 -0500
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.3.0

On 11/14/2017 03:35 PM, Max Reitz wrote:
> On 2017-11-14 21:30, John Snow wrote:
>> On 11/14/2017 01:46 PM, Max Reitz wrote:
>>> On 2017-11-14 19:45, Thomas Huth wrote:
>>>> On 14.11.2017 14:32, Max Reitz wrote:
>>>> [...]
>>>>> Well, do you want to document it?  I'd rather deprecate it altogether.
>>>> Maybe a first step could be to change qemu-img so that it refuses to
>>>> create new qcow1 images (but still can convert them into other formats).
>>>> So basically make qcow1 read-only?
>>> Yep, and the actual first step to that is to make it issue a deprecation
>>> warning when creating qcow v1 images (which is what I proposed). :-)
>>> Max
>> Deprecation warning is good.
>> In future versions you can shimmy it behind a
>> --no-really-I-want-this-old-format option, I think we ought to support
>> creating the images for as long as is technologically convenient.
> Well, at some point you can also demand from users to just dig out some
> old version of qemu-img to convert their qcow v1 images to qcow2.  It's
> not like they are going to miss out on anything.

As long is convenient. I won't throw a fit that it needs to be around
forever, but as long as it's sufficiently guarded from use and isn't
hard to keep around I'd prefer to do that.

I suppose it's just a weak preference.

> (If you deprecate emulated hardware, users may complain that they don't
> get the newest qemu features/bugfixes/... while continuing to use that
> hardware, so I can see that it's a tough decision whether to deprecate
> that.  But it's not like you are going to lose any features or anything
> if you convert your dusty images to qcow2.  On the contrary, we're
> helping you to get more performance out of them.  Maybe qemu should just
> silently convert qcow v1 images to qcow2 without asking the user, like
> Apple did...)
> Max

"Like Apple did" seems sufficient justification to never do that, but
maybe that's just my own opinion.

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