Clarification required reg., Redhat Cluster Suite

[Rick Stevens]

On Wed, 2006-06-07 at 09:13 +0530, GVSM Siva Kumar wrote:
> Dear Sirs,
> 	We have recently purchased Redhat Enterprise Linux ES version 3
> and Redhat Cluster Suite version 3 to establish a high availability
> cluster in Active/Passive configuration with shared storage.
> 
> 	As per documents available on Redhat's website, it is possible to
> establish a heartbeat mechanism over Ethernet. However, our system
> integrator feels that this is not possible with RHCS 3 and that heartbeat
> mechanism can only be established using a Quorum partition. The SI also
> believes that quorum based heartbeat is superior to Ethernet based 
> heartbeat mechanism.

I have no idea who your SI is, but he certainly has no idea what the
hell he's talking about.  The NIC-based heartbeat is used EXTENSIVELY
on HA clusters...the quorum mechanism is used far, far less often.

> 
> 	In this regard, can someone please clarify the following.
> 
> 1) Whether Quorum partition is a superior mechanism for establishing
> heartbeat? If so, then in what aspects?
>    (Somehow, this looks strange, in an ethernet based heartbeat only
> network latencies are involved, which must be negligible with a ethernet
> crossover cable. Whereas quorum partition involves two latencies in
> writing/reading the quorum partition and the disk access time itself.
> Surely, a crossover ethernet based heartbeat must be superior to quorum
> partition.) 

The quorum partition is NOT the preferred mechanism, and you've hit on
the primary reason...latency.

> 
> 2) Is it not possible to establish heartbeat using an ethernet/serial
> crossover cable?

Yes, you can use a crossover cable or a hub or switch.  Your choice.  I
would use a switch and set things up to use a multicast address
(224.0.0.x).  This allows you to expand the cluster easily...a crossover
cable limits you to a two-node cluster.


> 	sivakumar
> 
> 
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- Rick Stevens, Senior Systems Engineer     rstevens at vitalstream.com -
- VitalStream, Inc.                       http://www.vitalstream.com -
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-                    I doubt, therefore I might be.                  -
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