So what was the answer, part III
RAC is not Grid.
Grid is not RAC.
You can do “Grid” without RAC. RAC can be part of your “Grid” – (the use of many computers together as if they were more or less one larger computer). It doesn’t have to be – but it can be.
ASM can be part of your Grid. Slide storage in, slide storage out, move storage around if you need to. Transportable Tablespaces can be part of your Grid. Enterprise Manager Grid control – obviously (the name should help give it away) can be part of your Grid. Identity Management with centralized control over user identities, passwords, authorizations – can be part of it. In short, anything that helps you achieve the goal of “using many computers together as if they were more or less one larger computer” is part of it.
That seemed to help most people, as they assumed RAC is Grid is RAC is Grid. Simply understanding that RAC is not “Grid” and vice versa helped to clear up lots of confusion.
Then, we got down to talking about RAC and ASM. Why might the individual want to use RAC, what it would provide for them. It always came back to
- Ability to scale in a different way – instead of bigger and bigger machine, with more machines
- Availability, the capability to keep on running when a node in the cluster fails
- Flexibility in resource deployment, the ability to assign or reassign specific nodes to specific services (tasks)
ASM on the other hand, that was somewhat easier. It seems that the biggest user of disk is – well, the database. Having a bit more control over that resource doesn’t hurt. From the small system, where the DBA doesn’t know how to best utilize their six direct attach disks to a large system with dozens or hundreds of devices – ASM does make sense. The biggest confusion however was again “what is it”. I try to explain things simply – and the easiest way I’ve come up with for describing this is simply
“this is a database file system, it is a file system like any other file system – it is a file system that only contains database stuff however, it is a database file system. It is a database file system that provides redundancy if you need it, as well as database knowledgeable striping of data over all of your available devices”.
That is it – it is a file system. It has file system “drivers”, just like anything else. Once that was understood – it was easier to discuss the ins and outs of ASM.
In short, most of the time spent talking about ASM, RAC, Grid was spent defining terms. Which is actually quite important if you ask me.