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тАО07-14-2009 05:40 AM
тАО07-14-2009 05:40 AM
Recently we saw quorum lost situation and thought about adding another one. is that supported? Any one currently using two quorum disks?
openais[17753]: [CMAN ] lost contact with quorum device
openais[17753]: [CMAN ] quorum lost, blocking activity
Solved! Go to Solution.
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тАО07-14-2009 06:30 AM
тАО07-14-2009 06:30 AM
Re: is it possible to configure TWO quorum disks on Redhat cluster suit?
This is done at the beginning of cluster configuration.
http://www.centos.org/docs/5/html/5.1/Cluster_Administration/s1-naming-cluster-CA.html
I don't see in the interface an ability to configure two quorum disks.
A quorum disk needs to be accessible to both nodes, on shared storage.
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тАО07-17-2009 02:51 AM
тАО07-17-2009 02:51 AM
Re: is it possible to configure TWO quorum disks on Redhat cluster suit?
If having one quorum disk out of two would be acceptable, it would make the following scenario possible:
On node 1:
- Lost contact with node 2
- Errors with quorum disk A, but quorum disk B is still accessible
(errors are caused by node 2 accessing quorum disk A, but this node does not know the cause)
=> conclusion: node 2 is down and I have quorum, so this node can continue and take over the services of node 2
On node 2:
- Lost contact with node 1
- Errors with quorum disk B, but quorum disk A is still accessible
(errors are caused by node 1 accessing quorum disk B, but this node does not know the cause)
=> conclusion: node 1 is down and I have quorum, so this node can continue and take over the services of node 1
Overall result:
- both conclusions are incorrect
- Cluster is now in split-brain mode
- Massive filesystem corruption on shared disks
- Data loss
- Loss of hours of business when restoring backups and recovering
- Boss is very unhappy!
Lesson learned:
When the cluster gets split in two by connectivity problems, it is important that exactly *one* half can get the quorum.
Equally important is that the other half *must not* get the impression that it has the quorum too.
Therefore the quorum disk must be indivisible.
MK
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тАО07-17-2009 06:12 AM
тАО07-17-2009 06:12 AM
Re: is it possible to configure TWO quorum disks on Redhat cluster suit?
to break a tie among an even number of
cluster members. Using two quorum disks
would be seem to be about as useful as using
none, but would be subject to more problems.
> Having two quorum disks would [...]
Among other things, it would normally change
the number of votes required to reach a
quorum.
I don't know about Red Hat's cluster
documentation, but this is all covered in
considerable detail in the VMS documentation
(and has been for the past twenty years or
so).
http://h71000.www7.hp.com/doc/82final/6318/6318pro_020.html#quorum_strat
One thing is pretty clear there:
"Each OpenVMS Cluster system can include only
one quorum disk."
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тАО07-17-2009 08:10 AM
тАО07-17-2009 08:10 AM
SolutionI was looking into setting up a second quorum disk with RHCS 5.2, but so far don't know how. I don't know if it is allowed in RHCS 5.2. Anyone knows?
I was able to do so with RHCS 4.x.
To compensate for lack of second quorum disk, I complement quorum disk setup with a heuristics logic by pinging the gateway from clustered nodes. Exmaple:
In addition, I implement a combination of persisten scsi reservation and power fencing through ILO2 and RSA2 to ensure data integrity.
Cheers,
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тАО08-11-2009 12:13 AM
тАО08-11-2009 12:13 AM
Re: is it possible to configure TWO quorum disks on Redhat cluster suit?
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тАО08-24-2009 01:22 PM
тАО08-24-2009 01:22 PM
Re: is it possible to configure TWO quorum disks on Redhat cluster suit?
http://www.redhat.com/docs/manuals/csgfs/browse/rh-cs-en-3/index.html
Cheers