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Re: [dm-devel] [PATCH v3 0/4] dm-replicator: introduce new remote replication target



On Wed, 2009-12-09 at 05:39 -0500, Christoph Hellwig wrote:
> On Tue, Dec 08, 2009 at 12:42:27PM -0600, James Bottomley wrote:
> > Could I just echo Lars' statement.  With the upstream inclusion of drbd,
> > dm-replicator becomes a *third* replication system asking to be in
> > kernel.  It is definitely a kernel policy question of whether we want
> > three separate replicators, and so should be Cc'd to lkml so that people
> > interested in that can weigh in.
> 
> And unliley the previous two this one actually offers the benefit of
> beeing integrated with our major block device management framework.

md/nbd *is* integrated with a major block management framework.  The
fact that it's md not dm reflects the fact that it leverages the md
raid1 framework to perform the replication and merely uses nbd as a
remote block transmission pipe.  I'd submit this is the correct way to
do things.

The problem now is that the md raid framework isn't integrated into dm,
but I think someone else is looking at that ...

> Interesting that the question comes up now after I was shot down for it
> in the drbd discussion.

So the value add of drbd over md/nbd is symmetric active.  I think that
could be pulled into the md raid infrastructure as well, but someone has
to figure out how.

James



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