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Date: Wed, 23 Feb 2011 09:31:52 -0600
From: Anthony Liguori <anthony@codemonkey.ws>
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Subject: Re: [Qemu-devel] Re: Strategic decision: COW format
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To: Avi Kivity <avi@redhat.com>
Cc: Kevin Wolf <kwolf@redhat.com>, Chunqiang Tang <ctang@us.ibm.com>, qemu-devel@nongnu.org, Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>, Markus Armbruster <armbru@redhat.com>

On 02/23/2011 09:23 AM, Avi Kivity wrote:
> On 02/23/2011 04:23 PM, Anthony Liguori wrote:
>> On 02/23/2011 07:43 AM, Avi Kivity wrote:
>>> On 02/22/2011 10:56 AM, Kevin Wolf wrote:
>>>> *sigh*
>>>>
>>>> It starts to get annoying, but if you really insist, I can repeat it
>>>> once more: These features that you don't need (this is the correct
>>>> description for what you call "misfeatures") _are_ implemented in a 
>>>> way
>>>> that they don't impact the "normal" case. And they are it today.
>>>>
>>>
>>> Plus, encryption and snapshots can be implemented in a way that 
>>> doesn't impact performance more than is reasonable.
>>
>> We're still missing the existence proof of this, but even assuming it 
>> existed,
>
> dm-crypt isn't any more complicated, and it's used by default in most 
> distributions these days.
>
>> what about snapshots?  Are we okay having a feature in a prominent 
>> format that isn't going to meet user's expectations?
>>
>> Is there any hope that an image with 1000, 1000, or 10000 snapshots 
>> is going to have even reasonable performance in qcow2?
>>
>
> Are thousands of snapshots for a single image a reasonable user 
> expectation?  What's the use case?

Checkpointing.  It was the original use-case that led to qcow2 being 
invented.

Regards,

Anthony Liguori