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

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

Hi all, David,

I'm contemplating SCTP versus OpenAIS/corosync. Is dlm_controld(.pcmk)
pro-actively informed if a single ring/link goes down, as to trigger
faster SCTP recovery - or is it left for SCTP to time out on its own and
proceed?

If the latter - is there a way to auto-tune the SCTP time-outs to make
sure the DLM doesn't stall longer than that? I'm wondering whether
there's any chance for higher-level time-outs, ie a monitor operation on
a filesystem-using service.

RFC 5061 seems to support dynamic reconfiguration in such a fashion. If
I'm reading http://tools.ietf.org/html/rfc4960#page-87 correctly, SCTP
multi-homing is "active/passive", so there's some latency on the
fail-over at least. If several links go down at once, SCTP might try
them in sequence and pick the one surviving link last, incurring a large
latency.

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)?


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 ;-)


Regards,
    Lars

-- 
Architect Storage/HA, OPS Engineering, Novell, Inc.
SUSE LINUX Products GmbH, GF: Markus Rex, HRB 16746 (AG N?rnberg)
"Experience is the name everyone gives to their mistakes." -- Oscar Wilde