Cluster Lock VG - Exclusive or Shared Mode???

[Karthik S S]

Hi,

In a two node cluster we need to have atleast only Cluster Lock VG configured. My question is whether we need to activate this Lock VG in Exclusive mode or Shared mode (vgchange -S y .. & vgexport -s ... on node 1 / vgimport -s .. on 2nd Node)? To my knowledge when there is split brain scenario the cluster nodes try to acquire exclusive access to the Lock disk. Also I need to know what is the relevance of import VG in shared mode? I have never come across any application that needs the VG to be in shared mode.

Pl. clarify.

Thanks,
Karthik S S

[Hoefnix · Accepted solution]

Hi,

We have clusterlock disks definded that are member of a package volumegroup. So it does not have to be exclusive.

But you are talking about lock_VG, the only restriction I could find is that a lock_VG may not be a VG that is member of another cluster(sounds logic).

So, do you mean lock_PV or lock_VG?
I think both not have to be exclusive, but when a package is using it, it will use it exclusive.

HTH,
Peter

[melvyn burnard]

The cluster lock disc, and consequently tthcluster lock vg, must be availabloe on ALL nodes in the cluster.
It is usually a normal shared exclusive vg, where one of the data discs has the cluster lock info writtwn to it at teh time of cluster creation.
You can, however, have a vg that is seen by all nodes, with one PV in it which is hte cluster lock PV, but the vg is never activated except at the tim eof cluster creation, or re-writing the cluster lock info. But isn't that a waste?

And a VG that is truly shared (vgchnage -S y ) is used for Oracle parallel Server, or the newer Oracle RAC .

[Karthik S S]

I mean lock_PV ...

-Karthik S S

[Karthik S S]

Does the LOCK VG needs to be in activated mode when you modify the cluster configuration??

Thanks,
Karthik S S

[G. Vrijhoeven]

Hi Karthik,

If i rember correct the lock vg needs to be activated when you run cmapplyconf. But to check you can do a cmcheckconf. This will generate a message if you cluster lock vg is not activated.

HTH,

Gideon

PS. We use cluster lock disk and no cluster lock vg but when i read the documentation i can not find a difference. What is your reason to go for the cluster lock vg?

[melvyn burnard]

If the changes you are making to the cluster do not change the PV you are using for the cluster, then the answer is no.
The only time you need to do that are when you are changing the PV that will be used as the cluster lock, or the PV has been replaced, and a vgcfgrestore has NOT restored the cluster lock info due to a vgcfgbackup not being done after the cluster lock was written.

[Francois LAURENT]

Hello,

The shared activated mode (vgchange -s y) is only used in few case, and it's not a general used (as i know). Sharable mode means the vg can be reach by muliple node at the same time.

Normaly, the first_cluster_lock_pv and the first_cluster_lock_vg are defined by SG with cmquery comand (ie man : "the volume group and physical volume name of a disk chosen based on minimum failover time calculations")

For distributing binnary file :
###############################
1) Activate the cluster lock volume group so that the lock disk can be initialized:
# vgchange -a y /dev/vglock

2) Generate the binary configuration file and distribute it across the nodes.
# cmapplyconf -v -c \
/etc/cmcluster/cmclconf.ascii -P \
/etc/cmcluster/pkg1/pkg1conf.ascii

3)Deactivate the cluster lock volume group.
# vgchange -a n /dev/vglock


Just take care that the vg as defined as first_cluster_lock_vg is not in /etc/lvmrc file.