A long time ago I performed an installation of an Oracle cluster. This cluster, unlike other real clusters, is a cluster using RedHat Cluster Suite (RHCS) and involved two Dell 1950’s each with 8GB RAM and two 146GB 15K SAS drives. Each of these machines are connected to a CLARiiON SAN via QLogic FC cards through a pair of MC Data FC switches.
This cluster is more of an active/active cluster but, unlike Oracle’s RAC clustering software, there are four instances running on one machine and four running on the other; effectively evening out the load. There are quite a few downsides to this method which I will outline below. There are, however, a few pro’s as well.
- Allows for applications not written for RAC cluster to still be used in a clustered environment for High Availability.
- Expensive! RHCS was needed for this setup and GFS ($2000 per node per year) was needed. This company chose to use a supported version of Linux, Cluster Suite and GFS. Of course, you can do this freely as the OS, File System and cluster utility are all freely available.
- Not truly load balanced. This setup was meant to be load balanced but they are still two separate Oracle installations on two machines. The clustering suite just allows for proper failover.
- RHCS (Red Hat Cluster Suite) was never made to support Oracle on both systems. Oracle’s Enterprise Manager will not start for both installations on the same Ethernet adapter. This situation would be encountered if both installations would fail over to one machine. EM is inaccessible for the databases which failed over.
- Lots and lots of editing needed to be done to make Oracle work properly – editing the startup scripts, oratab, creating more custom startup scripts and more. In general this was a messy install.
In summary, I would not recommend using Oracle with RHCS. I would highly recommend that the application be re-written to be “RAC Compatible” so that you can fully utilize the power of Oracle load-balancing. This will save time and money in the short run and possibly the long run depending on what kind of support issues we might encounter. RHCS is great but I wouldn’t recommend it to anyone for Oracle.