Cluster Lock

[Leila Maria Rebel]

Hi!
I?ve a two-node local cluster, and I?m migrating to a Campus Cluster. My questions are:

1) Why do I HAVE to use dual cluster lock?

2) How to configure it:
a) On both node the same parameters for FIRST_CLUSTER_LOCK_PV=disk1 and SECOND_CLUSTER_LOCK_PV=disk2 ??

b) On each node different value for FIRST_CLUSTER_LOCK_PV=diskn ??

3) May I use any VG for CL, regardless which is its primary node? Getting the lock disk doesn?t mean mounting the vglock, correct ?

Thanks

Leila

[melvyn burnard · Accepted solution]

1) Why do I HAVE to use dual cluster lock?
To try to avoid the "Split Brain Syndrome"

2) How to configure it:
a) On both node the same parameters for FIRST_CLUSTER_LOCK_PV=disk1 and SECOND_CLUSTER_LOCK_PV=disk2 ??

b) On each node different value for FIRST_CLUSTER_LOCK_PV=diskn ??
The CL PVs will possibly be the same on the nodes, but not necessarily. The important thing is they are on vg's seen by ALL nodes in the cluster.

3) May I use any VG for CL, regardless which is its primary node? Getting the lock disk doesn?t mean mounting the vglock, correct ?
Correct.


To avoid using cluster lock discs, you may prefer to use an Arbitration node.

I suggest you take a look at:
http://docs.hp.com/hpux/onlinedocs/ha/hpworl98.pdf
and also:
http://docs.hp.com/hpux/onlinedocs/B3936-90045/B3936-90045.html

[Leila Maria Rebel]

1) Why do I HAVE to use dual cluster lock?
To try to avoid the "Split Brain Syndrome"

=> I understand that dual CL conf increases the possibility of having the Syndrome. Could you explain to me this situation? I visited yesterday both links you sent, but I still have doubts.

2) How to configure it:
a) On both node the same parameters for FIRST_CLUSTER_LOCK_PV=disk1 and SECOND_CLUSTER_LOCK_PV=disk2 ??

b) On each node different value for FIRST_CLUSTER_LOCK_PV=diskn ??
The CL PVs will possibly be the same on the nodes, but not necessarily. The important thing is they are on vg's seen by ALL nodes in the cluster.

=> Which configuration do you suggest? I think the "a" item reduces the possibility of having the Syndrome...

3) May I use any VG for CL, regardless which is its primary node? Getting the lock disk doesn?t mean mounting the vglock, correct ?
Correct.

=> Does it make sense having a mirror copy of the VGlock? I don?t think so ...

To avoid using cluster lock discs, you may prefer to use an Arbitration node.

=> I have to study this possibility. Thanks.

[melvyn burnard]

aha, got my fingers twisted there.
Sorry, the dual cluster lock is needed in case one entire side of the campus cluster, namely a data centre, goes down. The other site must be able to get a cluster lock disc. This INCREASES the chance of Split Brain Syndrome ( imust have had "Brain Asleep " earlier :-}

The physical disc device naming will differ or be the same DEPENDANT upon how you have.
configured your hardware. If you create the shared vg's, cmquerycl will attempt to check for a shared vg and list the PV's in the ascii file.
As for mirroring the CL info, this is not and cannot be done. The CL info gets written into an area that is Never mirrored, even thoough all Lvol's in the VG may be mirrored.

This is usually explained quite well in the ServiceGuard class.


HTH

[Leila Maria Rebel]

Ok, it seems perfect to me. Thanks a lot!

Leila