[Pacemaker] Does pingd works on openais?

[Pinto, Phil (GTI)]

Hi - just thought I would jump in here 

>The fact that links get broken completely, but both side can still reach
>the STONITH device, however is statistically very rare.  In fact,
>connectivity to the STONITH device becomes the "quorum token."

This may not always true in a virtual environment if two nodes are running under a VM and the VM in turn runs a virtual Stonith device.  



Thanks...
 
Phil Pinto 

-----Original Message-----
From: pacemaker-bounces at clusterlabs.org [mailto:pacemaker-bounces at clusterlabs.org] On Behalf Of Lars Marowsky-Bree
Sent: Friday, March 07, 2008 3:29 PM
To: The Pacemaker cluster resource manager
Subject: Re: [Pacemaker] Does pingd works on openais?

On 2008-03-07T12:30:27, Serge Dubrouski <sergeyfd at gmail.com> wrote:

> In fact I'm afraid that CRM lacks one feature that other clustering
> projects have. It's that quorum disk. In RedHat ClusterSuite or in HP
> ServiceGuard quorum disk helps to fight split brain scenario. 

That's not a CRM/Pacemaker-level feature though. That needs to be
provided by the cluster infrastructure below.

You're right that heartbeat does not have a disk quorum plugin. Xinwei
has written a disk-based comm plugin, but that wasn't submitted
upstream. (And, AFAIK, never shipped anywhere.)

> It's not clear how CRM acts when heartbeat link gets broken and nodes
> can't communicate to each other. What I see in my logs both nodes try
> to STONITH each other which isn't the best way to handle this
> problem.

The surviving side would still fence the other, so that's a partially
separate issue. 

The fact that links get broken completely, but both side can still reach
the STONITH device, however is statistically very rare.  In fact,
connectivity to the STONITH device becomes the "quorum token."

I'm not saying it wouldn't be nice to support disk-based comms/quorum
with heartbeat as well, but really it isn't a crucial feature.

> Please do not mistake quorum drive (feature for local cluster) with
> quorumd server which was designed for  geographically spread clusters.

I'm very clear on the distinction ;-)

Though this is not entirely true: it's essentially the same concept. A
3rd party tie-breaker is introduced to decide equal node count splits.
Quorum disk, or quorum server - it's the same idea; one scenario uses
TCP/SSL and the other SCSI reservations, that's the entire difference.
And if, as in this case, the SCSI reservation is in fact handled by the
iSCSI server (over TCP), the distinction becomes pretty much mood.


Regards,
    Lars

PS: And please, trim the quotes, if you would be so kind ;-)

-- 
Teamlead Kernel, SuSE Labs, Research and Development
SUSE LINUX Products GmbH, GF: Markus Rex, HRB 16746 (AG Nürnberg)
"Experience is the name everyone gives to their mistakes." -- Oscar Wilde


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