[Linux-cluster] Which lock manager to use on a 2-node GFS Cluster?

[Robert Peterson]

Celso K. Webber wrote:
> Hello all,
>
> Sorry for returning with a similar question: a few weeks ago, Bob 
> Peterson kindly answered a question of mine about selecting the right 
> lock manager. He added this answer to his Cluster Project FAQ:
> http://sources.redhat.com/cluster/faq.html#dlm_which
>
> The FAQ states that Oracle only supports GULM and not DLM.
>
> I had difficulties about setting up GULM under GFS 6.0 (RHELv3 based, 
> Linux kernel 2.4.x) because of the need of an even number of lock 
> managers. The GFS 6.0 manual states that you cannot use 2-node GULM 
> lock managers:
> http://www.redhat.com/docs/manuals/csgfs/admin-guide/s1-locl-gulm.html#S2-LOCK-GULM-NUMSVRS 
>
>
> The above section of the manual (section 8.2.2) states that you must 
> have at least 3 GULM lock managers for a high availability locking 
> systems under GFS.
>
> Question: is this still true under GFS 6.1 (RHELv4 based, 2.6.x 
> kernel)?  Since Oracle demands GULM, can I have a 2-node GULM GFS 
> locking system on a 2-node GFS Cluster?
>
> If not, which is the best option and which are supported by Red Hat?
> a) to have just 1 lock manager in one of the Cluster Nodes;
> b) to have just 1 lock manager in a machine outside the Cluster;
> c) to have 2 GULM lock manager on the cluster nodes;
> d) to have 3 or 5 lock managers using both the 2 cluster nodes and 
> other servers?
>
> Sorry for this recurring question, I wish to make sure of the correct 
> environment I should deploy for a customer who needs GFS (officially 
> licensed from Red Hat).
>
> Thank you all in advance.
>
> Celso.
>
> PS: I think this could be useful to be in the FAQ. What do you think Bob?
>
Hi Celso, Hirantha and everyone else,

Riaan's comments are correct (Thanks, Riaan!). 
I just made changes to the FAQ to hopefully clarify this.

Regards,

Bob Peterson
Red Hat Cluster Suite