On Mon, 13 Aug 2007, David Greaves wrote:
david@xxxxxxx wrote:
per the message below MD (or DM) would need to be modified to work
reasonably well with one of the disk components being over an unreliable
link (like a network link)
are the MD/DM maintainers interested in extending their code in this
direction? or would they prefer to keep it simpler by being able to
continue to assume that the raid components are connected over a highly
reliable connection?
if they are interested in adding (and maintaining) this functionality then
there is a real possibility that NBD+MD/DM could eliminate the need for
DRDB. however if they are not interested in adding all the code to deal
with the network type issues, then the argument that DRDB should not be
merged becouse you can do the same thing with MD/DM + NBD is invalid and
can be dropped/ignored
David Lang
As a user I'd like to see md/nbd be extended to cope with unreliable links.
I think md could be better in handling link exceptions. My unreliable memory
recalls sporadic issues with hot-plug leaving md hanging and certain lower
level errors (or even very high latency) causing unsatisfactory behaviour in
what is supposed to be a fault 'tolerant' subsystem.
Would this just be relevant to network devices or would it improve support
for jostled usb and sata hot-plugging I wonder?
good question, I suspect that some of the error handling would be similar
(for devices that are unreachable not haning the system for example), but
a lot of the rest would be different (do you really want to try to
auto-resync to a drive that you _think_ just reappeared, what if it's a
different drive? how can you be sure?) the error rate of a network is gong
to be significantly higher then for USB or SATA drives (although I suppose
iscsi would be limilar)
David Lang
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