[OpenAFS] R/W replication

[Dirk Heinrichs]

Nathan Neulinger wrote:
>=20
> Dirk Heinrichs wrote:
> >
> > Nathan Neulinger wrote:
> > >
> > > Dirk Heinrichs wrote:
> > > >
> > > > Derek Atkins wrote:
> > > > >
> > > > The reason I asked was that in case of inavailability of the "mas=
ter"
> > > > volume, clients cannot save their changes. There could also be an=
other
> > > > solution, that in case the server of the RW volume goes down, one=
 of
> > > > it's RO replicas will automatically be switche to RW, as long as =
the
> > > > original volume is down.
> > >
> > > That logic is fine so long as the volume is truly "down"... But wha=
t
> > > happens if it's just inaccessible on the network. A lot of people d=
o
> > > replicas geographically distributed, in which case, that condition =
will
> > > be relatively common.
> > It could be optional, on a per volume basis.
> >
> > Bye...
>=20
> Right, but what do you do in that circumstance?
>=20
> [client a][server b] ---/  /--- [client c][server d]
>=20
> if you have rw replicates on both servers, and the link between fails -
> a and b think they are fine, and c and d think they are fine. Who takes
> over as master? And what tells the other server that it is no longer
> master.
Ok, if it is the link that fails, and not one of the servers, you are
right. You would need some kind of conflict resolution. I wonder how the
Coda folks solved this. They support both disconnected operation and rw
replication. I think they use some kind of transaction processing
system, similar to  databases. Would be nice to hear from some practical
experience with this (maybe I'll have to ask on their mailinglist).

Bye...

	Dirk
--=20
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