[Cluster-devel] SCTP versus OpenAIS/corosync time-outs

[Lars Marowsky-Bree <lmb@suse.de>]

On 2009-11-02T08:41:43, Christine Caulfield <ccaulfie@redhat.com> wrote:

>> No concurrently active transmission ("rrp_mode active") - I wonder if it
>> is possible to put SCTP into such an mode, or, vice-versa, if this means
>> the DLM might be better off directly opening several TCP connections on
>> its own (and using them all at once, simply discarding duplicate
>> messages)?
> If you want to add TCP multi-homing code to the DLM, feel free. But it'll 
> be complicated and messy I promise. And it seems pointless to reimplement 
> all the sort of failover code that's already in SCTP for free.

Well, the thing is that active/active doesn't seem to be something SCTP
actually _can_ do, while quite obviously being the thing we'd want. I'd
love to be proven wrong about SCTP, of course, that'd make things
easier.

>> I'm not sure what kind of problems exist, if any, but this may be a
>> worth-while thing to consider or at least contemplate. I welcome
>> feedback ;-)
> To be honest, RRP & DLM/SCTP is not well tested or used. There are probably 
> lots of things that could be done to improve it. In particular the failover 
> aspect of it (the most important part of course) has probably not been 
> tried under any sort of serious load ... though i could be wrong.

Yeah, I'm trying to scope what needs to be tested and improved.

(Having OpenAIS+DLM run over bonding is mostly fine, but bonding is
sometimes the problem, and doesn't support all topologies; hence the
need to explore SCTP, or if SCTP can't do that, some alternative.)

A quite different trick for redundant networking would be to assign
static addresses to lo:X and run OSPF over all links, and having DLM
connect to the static IPs. That's quite trivial to setup, give us
"resilient" TCP (w/o needing to mess with SCTP, bonding, or anything).

Comments?


Regards,
    Lars

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