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CRS query [message #461595] Sat, 19 June 2010 08:57 Go to next message
dbanukesh
Messages: 96
Registered: November 2008
Location: London
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Hi guys,

Can you please help me understanding CRS concepts? my queries are:

1. Does CRS mounts SAN luns on Cluster nodes?
2. How does CRS interacts with ASM and Other Storage components.

If you can through some light on CRS functioning, that will be highly appreciated.

Many Thanks
Nukesh
Re: CRS query [message #461611 is a reply to message #461595] Sat, 19 June 2010 15:32 Go to previous messageGo to next message
BlackSwan
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Registered: January 2009
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http://www.oracle.com/technology/pub/articles/smiley_rac10g_install.html

Oracle Cluster Ready Services becomes Oracle Clusterware

Oracle RAC 10g Release 1 introduced Oracle Cluster Ready Services (CRS), a platform-independent set of system services for cluster environments.
In Release 2, Oracle has renamed this product to Oracle Clusterware.

Clusterware maintains two files: the Oracle Cluster Registry (OCR) and the Voting Disk.
The OCR and the Voting Disk must reside on shared disks as either raw partitions or files in a cluster filesystem.
This guide describes creating the OCR and Voting Disks using a cluster filesystem (OCFS2) and walks through the CRS installation.

[Updated on: Sat, 19 June 2010 15:33]

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Re: CRS query [message #461613 is a reply to message #461611] Sat, 19 June 2010 18:05 Go to previous messageGo to next message
dbanukesh
Messages: 96
Registered: November 2008
Location: London
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Thanks! One more doubt: does crs mounts san luns on cluster nodes? Pls reply

Thanks
Nukesh
Re: CRS query [message #461619 is a reply to message #461613] Sun, 20 June 2010 00:21 Go to previous messageGo to next message
trantuananh24hg
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dbanukesh wrote on Sun, 20 June 2010 06:05
Thanks! One more doubt: does crs mounts san luns on cluster nodes? Pls reply

Thanks
Nukesh


SAN Lun(s)? Does the OS maintain and control Lun? Or Does the SAN's manager program maintain and control Lun?

Anyway, I think, you should not locate the OCR & Voting Disk on the SAN. Avoid IO concurrently belong to the many server/machine owned the SAN.
Re: CRS query [message #461648 is a reply to message #461619] Sun, 20 June 2010 05:40 Go to previous messageGo to next message
dbanukesh
Messages: 96
Registered: November 2008
Location: London
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Ok Thanks. Is is mandatory to use OCFS2 in Linux/windows cluster environment for storing OCR and Voting Disk? sorry for these questions but since i am new to oracle rac, need to clear all my doubts. appreciate your valuable responses.
Re: CRS query [message #461653 is a reply to message #461648] Sun, 20 June 2010 08:32 Go to previous messageGo to next message
John Watson
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Registered: January 2010
Location: Global Village
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the 10g "Oracle Clusterware and Oracle Real Application Clusters Administration and Deployment Guide" includes this sentenceQuote:
Both the voting disks and the OCRs must reside on either cluster file system files or on shared raw devices that you configure before you install the Oracle Clusterware and RAC.
which I think makes it clear. Personally, I have never used OCFS for the voting discs or OCR, and I never will.
In fact, I will never use OCFS for anything. I see no purpose in OCFS from 10.x onwards, though I would be interested to know if anyone disagrees.
Re: CRS query [message #461673 is a reply to message #461619] Sun, 20 June 2010 21:02 Go to previous messageGo to next message
mkounalis
Messages: 147
Registered: October 2009
Location: Dallas, TX
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"Anyway, I think, you should not locate the OCR & Voting Disk on the SAN. Avoid IO concurrently belong to the many server/machine owned the SAN."

How exactly do you propose doing this? The OCR and Voting disks MUST be on shared storage - so what is wrong with having them reside on a SAN?

As John points out, OCFS2 is not needed - you can opt to place the OCR and Voting volumes on (shared) RAW disk partitions. John asks if there is any reason not to omit using OCFS2. There are a couple that come up.

The recomended size of the OCR and Voting volumes is 250mb. Depending on your SAN, it might not be possible to carve out luns or volumes that small. I have seen cases where the smallest lun was over a couple of gigs. So, if you have two OCR and three Voting (which in my humble opinion is the absolute minimum for a RAC cluster) then you could be using more disk space for these structures than would otherwise be necessary. If you created one or two OCFS2 filesystems to house your OCR and Voting resources, you may be able to cut down the amount of disk space needed to host these structures. While disk space is usually inexpensive, for some shops it is a premium. Older linux operating systems had a limitation for how many luns it would support. OCFS2 theoretically allows you to use one lun instead of five to support these structures. Modern linux kernels do not have this lun limit restriction - at least as far as I know.

With that said, I do agree with John that unless there is another compelling reason for doing so, implementing OCFS2 just for the purposes of hosting the OCR and Voting structures is not the best idea. You are having to maintain another stack of software and adding complexitity needlessly.

Just throwing in my $.02.
Re: CRS query [message #461676 is a reply to message #461673] Sun, 20 June 2010 21:22 Go to previous messageGo to next message
BlackSwan
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http://download.oracle.com/docs/cd/E11882_01/install.112/e10812/storage.htm#CWLIN312

"Desupport of Block and Raw Devices

With the release of Oracle Database 11g release 2 (11.2) and Oracle RAC 11g release 2 (11.2), using Database Configuration Assistant or the installer to store Oracle Clusterware or Oracle Database files on block or raw devices is not supported.

If you intend to upgrade an existing Oracle RAC database, or an Oracle RAC database with Oracle ASM instances, then you can use an existing raw or block device partition, and perform a rolling upgrade of your existing installation. Performing a new installation using block or raw devices is not allowed."
Re: CRS query [message #461679 is a reply to message #461676] Sun, 20 June 2010 22:42 Go to previous messageGo to next message
mkounalis
Messages: 147
Registered: October 2009
Location: Dallas, TX
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The poster asked about ocfs2 - so I assumed the target database version was 10gr2. . . . .

Where you mentioning the desupport of raw devices as another reason to implement ocfs2?
Re: CRS query [message #461704 is a reply to message #461679] Mon, 21 June 2010 01:54 Go to previous messageGo to next message
John Watson
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Registered: January 2010
Location: Global Village
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The way I have been looking at it, is:
Firstly, with 11.2 Oracle is clearly pushing us to use ASM for the voting discs and OCR. This certainly works and is straightforward to manage. Secondly, ASM disc groups have been the best storage (my opinion!) in terms of both performance and manageability, since it first came out (bearing in mind some early bugs.) Thirdly, the $OHs are probably best on local discs (another opinion.) Fourthly, NFS is supported now, through Oracle's NFS Direct drivers. Fifthly, if you need a clustered file system for non-database files and don't want to use a third party product, you can use ACFS. I haven't tried it on a production site, but it certainly works in the lab.
So I see OCFS as an historical anomaly: it was needed back in the days of 9i, when there was no ASM and clustered file systems were either expensive, or for some platforms, nonexistent.
I realize that I am going beyond the OP's original question, but I hope this does help him decide on OCFS, and I would certainly appreciate comment.
Re: CRS query [message #461740 is a reply to message #461704] Mon, 21 June 2010 04:35 Go to previous messageGo to next message
dbanukesh
Messages: 96
Registered: November 2008
Location: London
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Guys thanks for all your valuable feedbacks, it is much more clearer now that OCFS2 is not 'really' mandatory for configuring RAC either in 10g or 11g.- Correct me if i am wrong.

I have a 4-node cluster system configured (10g n RHEL 4) from my earlier DBA here and found out from the build document he has prepared that OCFS is not configured in the system. Since i just joined this project, i am trying to figuring out things here.
Re: CRS query [message #461777 is a reply to message #461740] Mon, 21 June 2010 07:47 Go to previous messageGo to next message
mkounalis
Messages: 147
Registered: October 2009
Location: Dallas, TX
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Ocfs has never been mandatory. Asm is the stated direction for storage from oracle. It would have been nice had you stated the target version of your database and why you were making the query in the first place - I think the answers you got assumed you were implementing - not checking an existing implementation..

John - The only reason I have come up with that makes sense to place oracle homes on clustered file systems and share them across nodes is if you are running a very large rac cluster. There you could put say five nodes into one home. Doing rolling upgrades would then be five at a time, but if you have thirty or fifty nodes then it makes sense. Otherwise I don't see any benefit to using shared oracle homes because then you loose the ability to do rolling upgrades - which I believe you were saying Wink.
Re: CRS query [message #461779 is a reply to message #461777] Mon, 21 June 2010 08:05 Go to previous message
dbanukesh
Messages: 96
Registered: November 2008
Location: London
Member

Thank you very much! all is clear now.
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