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Oracle RAC & ASM Hardware Setup

Posted on 2009-05-15
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Last Modified: 2013-12-18
Hello,

I'm looking into implementing an Oracle 10g RAC cluster with ASM storage for a project and there are a couple of issues I'm having in understanding the hardware configuration.

We have two database servers that we'd like to set up in an RAC cluster using ASM to control the file storage. Most of the Oracle documentation I've read speaks of the disks being stored separately from the database servers.

However, I was wondering if it's possible to use the hard disks of the servers that we have in the ASM disk groups, or if they have to be physically stored separately for proper clustering? This will mean that the database and ASM instance will be on the same node as the storage.

I've already searched other topics about RAC/ASM but I'm new to database clusters so I was hoping someone could clarify the issue.

Thanks for reading, any help would be much appreciated.

Nico
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schwertner earned 250 total points
ID: 24396993
If you use ASM you can use their   disk infrastructure and services for RAC.

It is more then clear that the RAC disks should be kept separately from the RAC nodes:
1. What will happen if the node (disks and RAC node) fails? Other nodes will not be able to use the database
2. ASN normally use a big disk farm with special interconnection (fiber channel)
3. The file structure of ASM is different as 'cooked' files. ASM uses 'raw' or OMF structure.

A complete discussion of all possible RAC hardware configurations is beyond the scope of this
remark. You want to have at least two and preferably three nodes for a RAC, each with redundant
power supplies, network cards, dual CPUs, and error-correcting memory; these are desirable
characteristics for any type of server, not just an Oracle server! The higher the number of nodes
configured in the cluster, the lower the performance hit you will take when one of the clusters
nodes fails.

The shared disk subsystem should also have hardware redundancy built inmultiple power
supplies, RAID-enabled disks, and so forth. You will balance the redundancy built into the shared
disk with the types of disk groups you will create for the RAC. The higher redundancy built into
the disk subsystem hardware can potentially reduce the amount of software redundancy you
specify when you create the databases disk groups.

Software Configuration

Although Oracle clustering solutions have been available since version 6, not until version 10g
has there been a native clusterware solution that more tightly couples the database to the volume
management solution. Cluster Ready Services (CRS) is the clustering solution that can be used on
all major platforms instead of an OS vendor or third-party clusterware.

CRS is installed before the RDBMS and must be in its own home directory, referred to as the
CRS_HOME. If you are only using a single instance in the near future but plan to cluster at a later
date, it is useful to install CRS first so that the components of CRS that are needed for ASM and
RAC are in the RDBMS directory structure. If you do not install CRS first, you will have to perform
some extra steps later to remove the CRS-related process executables from the RDBMS home
directory.

After CRS is installed, you install the database software in the home directory, referred to as
the ORACLE_HOME. On some platforms, such as Microsoft Windows, this directory can be a
directory common to all nodes, whereas other platforms, such as Linux, require OCFS version
2.x or later. Otherwise, each node will have its own copy of the binary executables.
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by:mrjoltcola
ID: 24398379
schwertner covers it well. I will re-emphasize, there is not much point in building a cluster if you are going to run your storage on the same node as one of the instances. The storage subsystem really needs to be on its own, with its own redundancy (EMC, NetApp, RAID). RAC is more for scale-out than redundancy, in my book, but the single point of failure, the storage, really needs the most attention in a RAC cluster, otherwise don't bother with RAC, use Data Guard or Streams.

For true, full redundancy, Data Guard physical standby is preferred. RAC lets you scale out gradually by adding more inexpensive nodes, but be advised, RAC administration is a whole new ballgame.


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Expert Comment

by:schwertner
ID: 24401506
There are many indications do not use ASM.
It adds license costs (this is an Oracle instance in his nature),
additional level of complexity (bugs, need education, trained personal),
delay due the additional level in data transfer.
I have met analysys that says what I briefly explain now.
Keep it simple and short (KISS!).
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Author Comment

by:RealtimeEngineeringLtd
ID: 24403314
Hi,

Thanks for such great responses.

The project we're working on is restriced to a standard license as far as I'm aware which would rule out data guard I think, please correct me if I'm wrong.

The setup is small, just two web servers and two database servers. I was investigating what the best solution for a clustering setup using oracle would be in this situation.

If the ASM instance requires its own Oracle license then that probably removes this option for us in terms of backing up the storage. It seems that ASM is overkill for this setup.

From schwertner's original comment I think that a RAID data setup should provide us with enough redundancy should a disk fail. The system isn't mission critical but I've been asked to research a clustering solution given the hardware and licenses we have.

Thanks again for the comments, I'm new to dbadmin stuff and your help is much appreciated.

Nico
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Assisted Solution

by:mrjoltcola
mrjoltcola earned 250 total points
ID: 24404057
Let me clear up confusion:

1) ASM is a standard feature of all Oracle editions, there is no extra license required.

2) ASM is just another logical volume manager. Take it or leave it, logical volume management can simplify things sometimes. Without ASM, you must manage RAW partitions for RAC.

3) There is no additional level in data transfer. The ASM instance just "manages" the logical volumes, but the primary instances do the actual IO, just like with cooked or raw configurations.

4) Finally, ASM is REQUIRED for RAC on Standard Edition. If you want to use raw fs for RAC, you need Enterprise.

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