Disk Lock and Quorum Server

[Karthick K S]

Pls Anyone Explain about use of Disk Lock and Quorum Server

[Robert-Jan Goossens_1]

Hi,

Check this doc.

http://docs.hp.com/en/B8467-90001/ch01s04.html

Regards,
Robert-Jan

[RAC_1]

The use of lock disk or quorum server is in servive guard. It helps to take care split brain syndrom. This is situation when cluster is coming up after reboot and evry node in cluster try to own it. With use of lock disk or quorum server other nodes know, the ownership is already taken and they just join the cluster.

[Rajesh SB]

Hi Karthick,

Just a collective info on

Lock Requirements
A one-node cluster does not require a cluster lock. A two-node cluster
requires a cluster lock. In clusters larger than 3 nodes, a cluster lock is
strongly recommended. If you have a cluster with more than four nodes,
a cluster lock disk is not allowed, but a quorum server may be used.

Cluster Lock
Although a cluster quorum of more than 50% is generally required,
exactly 50% of the previously running nodes may re-form as a new
cluster provided that the other 50% of the previously running nodes do
not also re-form. This is guaranteed by the use of a tie-breaker to choose
between the two equal-sized node groups, allowing one group to form the
cluster and forcing the other group to shut down. This tie-breaker is
known as a cluster lock. The cluster lock is implemented either by
means of a lock disk or a quorum server.
The cluster lock is used as a tie-breaker only for situations in which a
running cluster fails and, as ServiceGuard attempts to form a new
cluster, the cluster is split into two sub-clusters of equal size. Each
sub-cluster will attempt to acquire the cluster lock. The sub-cluster
which gets the cluster lock will form the new cluster, preventing the
possibility of two sub-clusters running at the same time. If the two
sub-clusters are of unequal size, the sub-cluster with greater than 50% of
the nodes will form the new cluster, and the cluster lock is not used.

See this use ful link on more info.
http://docs.hp.com/en/B3936-90065/ch05s02.html

Regards,
Rajesh

Regards,
Rajesh

[njia_1]

Hi

Disk lock is only supported by cluster with less than 4 nodes and the whole cluster has to be stoped to remove the disk lock if more nodes are added to it.

I had this problems before, adding 6 nodes to a 4 nodes cluster, stop the cluster and then adding all the new nodes and start the cluster again.

Quorum does not have this limitation, but it could be the single point of failure.

[melvyn burnard]

A cluster can use a form of arbitration, known as cluster locking, using either a disc method, or a Quorum Server method.
This arbitration is ONLY used when a failure of some kind occurs that results in EXACTLY 50% of the cluster nodes are left, and are attempting to perform a cluster reformation.

One uses a physical disc that must be accessibla from ALL nodes in the cluster, but is not supported in clusters that have 5 or more nodes.
Quorum Server is software based, installed and running on another server OUTSIDE of the cluster, contactable via the network.
QS is supported in a cluster of any size, and a QS server can support 50 clusters or 100 cluster nodes, depending on which limit is reached first.

[Devender Khatana]

Hi,

Lockdisk -> As stated earlier it is a shared disk which is marked as the breaker for all nodes in the cluster. It can be used for only upto 3 node cluster. Wheneven there is a hearbeat miss and the nodes are not be able to communicate to each other, all of them tries to obtain the control over the lock disk, the nodes which takes control of the lock disk continues to run the cluster and the nodes which are not able to communicate with this node performs TOC.

When no. of nodes increase to more than 3 a lock disk is not helful and a quorum server shall be used to perform the same function.

HTH,
Devender

[Karthick K S]

Thanks For all Comments