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



On 10/04/2012 10:44 AM, Bryn M. Reeves wrote:
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On 10/04/2012 11:17 AM, Mark Woodward wrote:
I was going to try to answer in line, but decided that it would be
too much work. There are utilities to extract the exception table
out of the LVM2 snapshot, and if you can code in almost any
language, you can write your own. It is dead simple. You can google
for ddsnap and zumastore to
ddsnap was the Zumastor snapshot tool which uses a different in-kernel
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.
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


The format of the array is simple: old_address (The offset in the
volume) followed by the new_address (the offset in the COW device).
An array of all the "old_address" values is the changed block list.
You don't even need to worry about the data if you can really get a
file list by blocks.
If you really want to poke into the CoW store format I'd start by
reading dm-snap-persistent.c which is the traditional device-mapper
snapshot format.

Snapshots using the thinp target use the metadata format described in
dm-thin-metadata.c.

Where are these files to be found?

Regards,
Bryn.
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