lock disk

[gany59]

Hello Gents,
what is lock disk in a cluster.
is this is required in every cluster environments, and how to do the lock disk in a cluster.

Thanks in advance!!!

[Torsten.]

In simple words: The lock disk helps to decide which "half" of a cluster survives if the nodes cannot see each other. Who gets the lock, who survives. You can use shared disk as lock or a quorum server.

[stephen peng]

the following messages came from "Managing ServiceGuard":
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.

If you have a two-node cluster, you are required to configure a cluster lock. If
communications are lost between these two nodes, the node that obtains the cluster
lock will take over the cluster and the other node will halt (system reset). Without a
cluster lock, a failure of either node in the cluster will cause the other node, and therefore
the cluster, to halt. Note also that if the cluster lock fails during an attempt to acquire
it, the cluster will halt.

regards
Stephen

[Torsten.]

It's required as long as you don't have a quorum server and it is configured in cluster config file.

[melvyn burnard]

take a read of this:
http://bizsupport1.austin.hp.com/bc/docs/support/SupportManual/c02056095/c02056095.pdf

[Raj D.]

Gany,


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, lock LUN, or a quorum server.


- Lock disk is needed for setting up a 2 node cluster. more than 2 node cluster you may not need a lock disk, but a quorum server has to be there.

- Lock disk is a disk (Physical disk/lun) presented to both the server in the service guard. , and need to specify in the cluster configuration file under FIRST_CLUSTER_LOCK_VG & FIRST_CLUSTER_LOCK_PV

- To create a lock disk.
a. Get a lun presented to both the system.
b. on pri node: pvcrate, vgcreate it.
c. Specify the disk in the cluster.ascii file.
d. setup the cluster. Begin with cmquerycl.






Example :
Portion of a cluster.ascii file:

...
# Cluster Lock Device Parameters. This is the volume group that# holds the cluster lock which is used to break a cluster formation# tie. This volume group should not be used by any other cluster# as cluster lock device. FIRST_CLUSTER_LOCK_VG /dev/vg_ops # Definition of nodes in the cluster.# Repeat node definitions as necessary for additional nodes. NODE_NAME node1 NETWORK_INTERFACE lan0 HEARTBEAT_IP 15.13.171.43 FIRST_CLUSTER_LOCK_PV /dev/dsk/c1d0s2
...




Cheers,
Raj.

[Raj D.]

Gany,

Further reading: (Managing Service Guard)
- checkout cluster lock and lock requirement:

http://docs.hp.com/en/B3936-90117/ch03s02.html#babbgfdh

Cheers,
Raj.

[Suraj K Sankari]

Hi,

Download or open this pdf file from the below link and go to page 66 for more information on lock disk.

http://docs.hp.com/en/B3936-90117/B3936-90117.pdf

Suraj