[Date Prev][Date Next]   [Thread Prev][Thread Next]   [Thread Index] [Date Index] [Author Index]

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:
-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

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.

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.

Sorry, I got pulled away a bit.

Let me understand. The CoW format changed, but the header signature stayed the same? I'm having a bit of an issue understanding this. The "old" LVM format CoW device had the signature "SnAp" and that had a fairly well understood layout. Has this or has this not changed? I had some code that worked in the 2.6 series of kernels using the LVM tools. However, when I run it on a later kernel version (3.2.0) it seems not to work. I am more than willing to say its a bug on my end, but can you clarify whether or not it is expected that this format would change? I am planning a server upgrade and I rely on the snapshot format for my differential backup tools.

As for the thin provisioned snapshot I have been long waiting for this. Is it "production ready?" if so, in what kernel version moving forward?

Regards,
Bryn.
-----BEGIN PGP SIGNATURE-----
Version: GnuPG v1.4.12 (GNU/Linux)
Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org/

iEYEARECAAYFAlBtoLQACgkQ6YSQoMYUY95MgACdFnOXbJC03HjQA8/p8kKxXeLD
ALMAmQFhD+OfKiA2YV9RS3kaUGFzvzE0
=wsdZ
-----END PGP SIGNATURE-----


[Date Prev][Date Next]   [Thread Prev][Thread Next]   [Thread Index] [Date Index] [Author Index]