Re: [linux-lvm] ANNOUNCE: an experimental implementation of snapshot merging

["Brian J. Murrell" <brian@interlinx.bc.ca>]

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On Tue, 2008-06-03 at 15:43 -0500, Chris Cox wrote:
> 
> I would think this would be VERY hard to do since both the "origin" and
> "snapshot" change (file deletes, etc).

I don't think it's as difficult as you are thinking it is.  You are
thinking of synchronizing filesystems, at the filesystem level, but
merging a snapshot back up into the origin does not deal with files or
even filesystems.  It deals with block devices and blocks, and is really
nothing more than a coordinated:

for each COW_block in snapshot; do
    for other_snapshot of origin; do
        copy origin[COW_block] to other_snapshot[COW_block]
        copy snapshot[COW_block] to origin[COW_block]
    done
done

> Do you have a set of rules you
> use for the merge?

There is no filesystem level merge.  There are no rules needed.

b.


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