Oracle RAC v/s Oracle DB

[Former Member]

Hi All, In my landscape some systems has oracle RAC and some has Oracle as the database for SAP landscape. What is the major difference and or advantages of having and Oracle RAC..considering clustering feature is available with OS host level as well. Would also like to know who do I know from OS, DB as well as SAP level(using transaction DB02) to know whether DB is oracle or Oracle RAC. I checked blogs but no clear answers I found so far. Please help. Regards, Vicky

[Brindavan_M]

Hi Vicky,

The Oracle RAC which stand for Real Application cluster.  The main objective of RAC Performance,scalability & Resilience

The oracle RDBMS have files and process

Files

• Data file
• Control file
• redolog file

Instance

• process manage memory
• process to manage IO
• maintenance & other process

In RAC environment one or more instance process will communicate single database not the files.

But, OS level cluster means that filesystem oracle file and other etc.. which exit and if its failed then it  will communicate to other OS database that mean OS cluster can be used  . You have to check the RAC instance in OS level as well in SAP.

Thanks,

Brindavan M

[fidel_vales]

Hi,

sorry but I do not agree with some of the things.

The main reason SAP (and Oracle) customers install Real Application Clusters is because it provides high availability at instance level. You can add ASM to increase the HA (but it does not replace other HA solutions like dataguard)

RAC can provide only scalability if you have CPU bottlenecks and there is no bigger "server" available.

RAC does not have to provide performance improvements. and this is a big misconception lot of people has. A lot of times it comes with performance degradations that have to be addressed with special tuning. It also comes with its own overhead (which usually is compensated with the less disk reads but ...)

The following comment is not correct (or not properly explained)

In RAC environment one or more instance process will communicate single database not the files.

RAC is supossed to be more than one server, it does not have sense to have only one RAC node (only on case of downtime). It is a SHARE storage solution. Several instaces share/access to the same database. One file (datafile, redo ...) belongs to one database so all instancess have fully access to all datafiles of the database.

I strongly recommend you to check the oracle documentation: https://docs.oracle.com/cd/B28359_01/rac.111/b28254/admcon.htm

that way you can avoid half explanations