[linux-lvm] access or interface to list of blocks that have, changed via C.O.W.?

[Bryn M. Reeves]

On 10/04/2012 11:00 PM, Stuart D Gathman wrote:
> On 10/04/2012 11:02 AM, Mark Woodward expounded in part:
>>
>>> snapshot target and metadata format. It does not share code with
>>> current (or historic afaik) LVM2/device-mapper and has been dead for a
>>> number of years (last commits around 2008).
>>>
>>>> get the code. It old and not supported currently, but still works.
>>>> I
>>> Really? I'd be surprised if it even builds against modern kernels or
>>> device-mapper.
>> ddsnap was the Zumastor snapshot tool which uses a different in-kernel
>> Well.....
>> The LVM2 code that ships with most distros still uses the old 
>> interfaces and still (Ubuntu 12.04) seemst to create a COW file with SnAp
> 
> This utility (ddsnap work alike) requires no kernel changes, and only 
> depends on the layout of the COW (and only on the changed block table):
> 
> http://www.opensvc.com/init/default/doc_storage_dds

This is closer to the kind of thing that Linda was originally asking
about. It seems to let you extract deltas and move them around and
re-apply them for replication purposes so it's similar to ddsnap in that
it's distributed although as you say it's entirely in userspace and
doesn't requite the ddsnap device-mapper target.

Regards,
Bryn.