[dm-devel] [RFC] dm snapshot based asynchronous replication

[Jonathan Brassow]

On Apr 16, 2009, at 2:02 AM, Lars Ellenberg wrote:

> On Wed, Apr 15, 2009 at 08:31:44PM +0200, christophe.varoqui at free.fr  
> wrote:
>>> Should I understand there's no way for userspace to extract from  
>>> the device mapper the cow'ed chunk list of a vanilla snapshot ?
>>
>> Replying to myself, I found an instructive post from Lars of the  
>> drdb folks : http://markmail.org/message/7qdbp36tohasojuy (thanks  
>> for sharing Lars)
>>
>> This script is easy enough to morph from its original snapshot  
>> reverting purpose to the replication model using the cow device as  
>> a changelog I described.
>>
>> Thanks for the inputs. I'll keep posting if I something of general  
>> interest comes out of this stuff.
>
> that perl hack was meanwhile ported to C by someone.
> posted earlier this year on dm-devel.
> also please do not ignore the Zumastor work.

It also seems that the script is not generic enough to handle the  
variety of exception stores that are coming.  I just wrote a 'snapshot- 
merge' target that will do what you ask.  I will post the patch  
shortly.  However, this won't help you in RHEL5.

  brassow