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



hi Hirantha

short answer: "No"

If you are willing to settle for "should work just fine" instead of "certified by Oracle" you can try running DLM on 2 RAC/GFS nodes, then "yes"

To have your solution certified/supported by Oracle, for a minimal configuration you need 5 machines:
a) 2 GFS/RAC nodes
b) 3 external GULM lock servers

We also found these system requirements somewhat excessive (having more lock servers than actual GFS-accessing cluster nodes).

more notes:
- supported GFS with RAC is GULM only - DLM is not supported by Oracle, because it is embedded by default.

- external lock servers - that means the the GULM service cannot run on the nodes accessing the GFS. The 3 GULM nodes and the 2 GFS/RAC nodes must be completely separate

- the reason for the separation of lock servers from GFS/RAC nodes is that Oracle RAC is designed to be able to with a single node up, whereas DLM needs a quorum of 50%+1 to operate. Also, external lock servers allow you to reboot any RAC node without causing the lock server to switch.

- specs for the locks servers are as entry-level as you can get for
modern server hardware, e.g. 1CPU, 1GB RAM.

- Red Hat Knowledge base article for RAC on GFS: http://kbase.redhat.com/faq/FAQ_78_3853.shtm It mentions GFS 6.0, (slightly out of date) but is just as relevant for GFS 6.1 / RHEL 4). According to this article, "Red Hat does not charge for Red Hat GFS nodes that are used only for the external lock server configuration"

- the Cluster/GFS FAQ has some URLs for RAC on GFS:
http://sources.redhat.com/cluster/faq.html#gfs_oraclerac

- MetaLink Note 329530.1 is the definitive source for what exactly is supported by Oracle, w.r.t. RAC and GFS. Unfortunately it is only available via Metalink.

Celso - answers to your questions below

Hirantha Wijayawardena wrote:
Hi,

I also wanted to post the same question on Bob post. But I given-up to ask
'cause it written as " DLM should work just fine." From the clause "Right
now, Oracle and Oracle RAC are only certified to work with the GULM locking
manager. So Oracle won't support your configuration if you're using DLM.
However, DLM should work just fine. Also, GULM has works fine on more than
32 nodes."

I just wanted to know was whether we could run Oracle or oracle RAC on
2-node cluster with DLM

Thanks in advance

- Hirantha



-----Original Message-----
From: linux-cluster-bounces redhat com [mailto:linux-cluster-
bounces redhat com] On Behalf Of Celso K. Webber
Sent: Wednesday, August 16, 2006 8:09 AM
To: linux clustering
Subject: [Linux-cluster] Which lock manager to use on a 2-node GFS
Cluster?

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?


No

(for purposes of my answer, I assume you mean GFS nodes when you write cluster nodes)

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;
Supported by Red Hat. Not supported by Oracle. Lock manager is a single point of failure

b) to have just 1 lock manager in a machine outside the Cluster;
Supported by Red Hat. Unsure if supported by Oracle. Lock manager is still a single point of failure

c) to have 2 GULM lock manager on the cluster nodes;
Not possible. you need 1 (minimum) or 3+ (recommended)

d) to have 3 or 5 lock managers using both the 2 cluster nodes and other
servers?
Have 3 lock managers external to the GFS nodes. the GFS nodes may not run the GULM server (neither primary nor standby) for it to be supported by Oracle.

This is your best option in terms of support, redundancy, etc, if not the most cost-effective.



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?

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org:Obsidian Systems;Obsidian Red Hat Consulting
email;internet:riaan obsidian co za
title:Systems Architect
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tel;fax:+27 11 792 6522
tel;cell:+27 82 921 8768
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url:http://www.obsidian.co.za
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