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

[Riaan van Niekerk]

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It mentions GFS 6.0, (slightly out of date) but is just as relevant for 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 at redhat.com [mailto:linux-cluster-
>> bounces at 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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