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1. Is ASM manadatory for RAC?yes
For non exadata systems ASM is not mandatory. There are clustered filesystem solutions which are supported.
On Exadata as you stated (in Question 2) ASM in a RAC configuration is mandatory to provide shared storage on the cells to the databases.
from which release of oracle it is manadatory?On Exadata only 11gR2 versions are supprorted.
2. I know ASM is manadatory for EXadata and RAC is not manadatory for Exadata , is my understanding correct?I guess you mean you can create normal RAC dbses, RACone dbses or even single instance dbses on Exadata?
Still you need the RAC on Exadata for ASM as explained in Quetsion 1.
3. I think ASM is included with the Clusterware software from 11gR2 onwards, what about the prior releases?ASM was introduced in Oracle 10g and was originaly part of the database source software.
On non-Exadata RAC systems, ASM is not required for storage. There are many other clustered filesystems that are supported for oracle datafiles, including OCFS2 and NFS. Most shops use ASM now, because it's so easy to implement, and is the standard for RAC systems. ASM was introduced in 10g, and was included with the database binaries. Starting with 11gR2, ASM was included with clusterware in a new software package, grid infrastructure. Grid infrastructure can be installed in either a standalone (oracle restart) or RAC configuration.
While RAC is not required for Exadata, ASM is required. It's the only method for accessing the disks on Exadata storage servers. If you chose to completely eliminiate RAC from your Exadata configuration, you could install grid infrastructure in standalone mode on each compute node. If you went this route, you would have to create separate griddisks for each compute node, as a diskgroup couldn't be shared between them. I wouldn't recommend this, as it will put constraints on your disk layout. You'll end up in trouble if one of your databases outgrows the diskgroup you've assigned it to. The other option would be to install grid infrastructure as a cluster and create single instance databases. Diskgroups would be shared between all of the compute nodes, because there is a clustered ASM instance spread between them.
This configuration can be created, even if RAC is not licensed. Oracle clusterware (including ASM) is available free of charge on any platform with a licensed oracle database (http://docs.oracle.com/cd/E11882_01/license.112/e10594/editions.htm#BABDJGGI). With this configuration, you also get the ability to perform a "cold failover" where if a compute node crashed, you simply have to start the database on another node, since the files are all available within ASM. If you're using the scan hostname in the connect string for the clients, nothing has to change from that end.
One thing to keep in mind with the second configuration is that while you haven't licensed RAC, your system will still be running like a RAC cluster, but without RAC databases. You'll still have to be familiar with RAC administration concepts (SCAN, srvctl, crsctl, etc).
udayjampani wrote:1) It no mandatory for RAC you can use other available volume managers which are available in market.
1. Is ASM manadatory for RAC , if yes from which release of oracle it is manadatory?
2. I know ASM is manadatory for EXadata and RAC is not manadatory for Exadata , is my understanding correct?
3. I think ASM is included with the Clusterware software from 11gR2 onwards, what about the prior releases?
2) Yes your understanding is correct. You can have 8 or more single node databases on 8 separate node respectively. Its all depends upon the customer environment how he want to use this.
3) Grid infrastructure was introduced in 11gR2 onwards. So you have cluster + ASM in single grid home.