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Redhat Clusters = single node database access
RAC Cluster = multi-node database access.
RHC means that your databases cannot take advantage of any type of any parallel processing or high-availability features that are available in O-RAC. One thing I would never do is mix the two. With RAC, I can also do a rolling upgrade of a database. You cannot do that wih RHC. As a former sys-admin/SAN admin and hardware field engineer, if I am standing up a system for Oracle, I would use an ALL ORACLE solution when it comes to clustering and high-availability - again if this is for Oracle high-availability solution. A side benefit of this redundancy is parallelism. I worked at a telco where having a RAC cluster for our DW solution doubled/trippled the ingest rate. You will not get that sort of bump using RHC.
When discussing this with your Oracle sales person, remember, EVERYTHING is negotiable. There is a lot of competition out there.
the things I would make sure you get included in your licenses are RAC, OEM management and tuning packs. They cost Oracle nothing to include the mgmt/tuning packs and as a matter of fact could reduce their cost by reducing the number of calls to Support when a junior DBA needs to figure out blocking issues, memory usage issues, cpu usage issues etc... I would say that including them can reduce the number of calls to support, but that is just me (former Oracle support, DEC Rdb support engineer, circa early 90's).
At the moment we have a project which use 1 Oracle standalone server(2CPUs, 96GB ram) with 4 Oracle Instances and aproximately 30users(80-250GB) connected to application servers.
--> 1. At the moment, you are using only One Oracle standalone server(2CPUs, 96GB ram).
1. If downtime is available, configure Active-Passive Configuration for Oracle Standalone Server. If something goes wrong for Active machine atleast all the 4 instances will failover to Passive Machine then Passive Machine will be active machine for all your 4 instances. For this setup you require only one Physical Server. Oracle Licenses are not required.
2. Check AWR/StatsPack report in peak time. So that you can suggest Application Team to fine tune the most problematic queries. So that atleast for time being you can reduce your CPU percentages from 100% to some minimal number.
3. Instead of going to 3-Node RAC - First implement Oracle Data Guard for this environment. So that if primary server not available for some reason your Standby Server will come up as a Primary Database within Minutes. For this you need One physical Server with only Oracle Licenses for Standby Database Server.
4. Any application before moving to either 2-Node RAC or 3-Node RAC, Application Team has to test all the functionalties. Without testing the Application in RAC moving to RAC is bit difficult.
Hope it helps....
If any further communications please feel free to post
At the moment we have only 3 applications servers connected to that server, but what will happend if I will connect next 26 ? I`m affraid that DB server will stop working...
Almost certainly. If you are experiencing problems with just 3 app servers, then adding additional application servers will grind the database down to a halt.
If you want to move to RAC then the application will need to be tested accordingly to ensure it handles RAC related errors.
To answer first your question regarding performance:
Having multiple servers hosting RAC can alleviate your issue with performance but of course this depends on how much cpu and memory you allocate to each host.
If you want to stay on a standalone database you can increase the cpu/memory to handle the workload.
The DBA's/developers should be looking at ways to tune the database. The fact you have multiple large schemas should not prevent them from doing this. I suspect this is where you would most likely have your biggest win.
A RAC be it 2 node or 3 node will give you availability in the true sense of the word and is what RAC was designed for.
An active/passive cluster will give you some sense of availability but of course if you have a failover due to a server/database crash then you will have downtime for the duration of the failover. So you will have some hardware just sitting there doing nothing for 99% of the time. However this will save you on the cost of RAC licenses.
All the best.