quorum disk & it's use.

[ani007]

Hi,
Can any one please explain the following question in an easy way...

What is quorum disk. What is the advantage when we use it in cluster environment. What is try breaker.

[Hein van den Heuvel · Accepted solution]

Tie Breaker - not Try Breaker. That's cute though!
http://en.wikipedia.org/wiki/Tiebreaker

In the beginning there was darkness.
Then 2 systems get booted 'at the same time'
There is no light and they can not yet see each other.
They each declare 'I'm in control of cluster X'.
Who wins?
Who get's to be created cluster X?
The first one 'reserve' the quorum disk and thus have more votes for its team.

11.5 Quorum Strategies
http://h71000.www7.hp.com/doc/732final/6318/6318pro_019.html

http://h71000.www7.hp.com/openvms/journal/v2/articles/cluster.html

http://www.hpl.hp.com/hpjournal/dtj/vol7num4/vol7num4art6.pdf

[RBrown_1]

Are you in the right place? Your other questions about quorum have been in the HP-UX and Linux forum.

In a VMS cluster, each system gets a number of votes. The total number of votes of all the systems in the cluster is EXPECTED_VOTES. When a system is up, it votes (if it is down, it does not vote). When the votes of all the running systems add up to more than EXPECTED_VOTES/2, then the cluster runs. If the number of votes drops to EXPECTED_VOTES/2 or less, the cluster stops running. It either waits for more votes to arrive, or its member systems crash, depending on how long there are not sufficient votes.

If you have only two systems in a cluster, there are only two ways do distribute the votes:
o they can each have the same number of votes
o one can have more votes than the other

If you want the cluster to stay up when one of the systems is down, then the remaining system must have more votes than the one that is down.

But if you want the cluster to stay up no matter which single system is down, then the only way to configure it is to:

1. give each system the same number of votes
2. supply a single disk drive with a direct connection to each system
3. designate this disk drive to be a quorum disk and give it some votes. This quorum disk supplies enough votes so that the votes from a single system plus the votes from the quorum disk > EXPECTED_VOTES/2.

You ask "What is a tie breaker?"

When you have the same number of votes to stay up as to go down, you have a tie (just like when two teams in a match have the same score). To break the tie, somebody needs to get more votes. The quorum disk provides the tie breaker votes.

hth

[P Muralidhar Kini]

Hi Anirban,

A Quorum disk acts as a virutal cluster member. i.e. it would be able
to contibute a vote just like any other cluster member.

You can refer the following link for more details -
http://h71000.www7.hp.com/doc/731final/4477/4477pro_002.html

Regards,
Murali

[pavaman_1]

Hi,

In short - Quorum Disk contains the cluster state and timestamp information. It allows continuous cluster availability without user intervention by configuring arbitrary parameters which provides each cluster member the flexibility in handling network failure or under a scenario when majority of the cluster members fails.

Pavaman

[Shriniketan Bhagwat]

Hi,

The quorum disk acts as a virtual cluster member whose purpose is to add one vote to the total cluster votes. By establishing a quorum disk, you can increase the availability of a cluster; such configurations can maintain quorum in the event of failure of either the quorum disk or one node, and continue operating.

Refer OpenVMS cluster systems manual from below link for more details.

http://h71000.www7.hp.com/doc/os73_index.html


Regards,
Ketan

[P Muralidhar Kini]

Hi Anirban,

I assume you have asked this question because you want to configure a
cluster. If yes, then how many nodes would be there in the cluster?

Generally setting up the quorum disk is recommended only for cluster
configuration where in there are only 2 nodes. If there are more than
2 nodes in the cluster then its not recommended to have a quorum disk.

Regards,
Murali

[ani007]

Actually i go through books but not able to understand.All off you help me to understand.Thanks every one.

[ani007]

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