[Pacemaker] Pacemaker cluster: OpenAis communication channels

[Florian Haas]

Steve,

what has repeatedly come up is that RRP links don't auto-heal (see
thread:
http://oss.clusterlabs.org/pipermail/pacemaker/2009-May/001784.html),
and that passive mode RRP seems to not work at all (see thread:
https://lists.linux-foundation.org/pipermail/openais/2009-October/013095.html
-- this was also heavily discussed on IRC; the only approach that fixed
the issue was to change rrp_mode to active). Can you fill us in on the
progress on these issues? Thanks!

Cheers,
Florian

On 10/22/2009 06:14 AM, Steven Dake wrote:
> You can run with one NIC (and switch) but then your NIC and switch
> become a SPOF (single point of failure).  Vehicles have a spare tire for
> a reason :)  If a NIC fails it may be ok to switch a service to a
> different node.  If a switch fails, The entire cluster becomes disabled
> until the switch returns to operation.
> 
> Availability is a mathematical equation: 
> 
> A = MTTF / (MTTF+MTTR)
> 
> Pacemaker improves availability (A) by reducing mean time to repair
> (MTTR) using failover while keeping the mean time to failure (MTTF)
> essentially the same (although it is generally a bit lower because of
> other components in the system required to introduce redundancy).
> Instead of a typical 1 machine MTTR of 4 hours under a typical SLA, MTTR
> may be 5-10 seconds or less (the time to failover the application and
> restart it).  If MTTR is several days to service a switch, your
> availability may not meet your customer SLA obligations.  When
> determining whether to use a redundant switch the risks vs cost have to
> be evaluated based upon your availability requirements.
> 
> Regards
> -steve

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