Re: Oracle 10g RAC Question

From: Howard J. Rogers <howardjr_at_dizwell.com>
Date: Tue, 05 Oct 2004 06:47:42 +1000
Message-ID: <4163091b$0$23894$afc38c87@news.optusnet.com.au>

Dusan Bolek wrote:

>> 1) Is 10g RAC basically the parrallel server of old? Thus I am
>> assuming that all disk devices must be seen by all nodes in the
>> cluster and also must be using raw disk devices for storage? (or even
>> better, for example: Can node1 see disk group X, and node2 see disk
>> group X & Y, and then node 3 see disk group Y & Z. Can 10g RAC
>> function in that type of config? My purpose would be to segregate the
>> different applications so that they use specific nodes in our RAC, and
>> thus an SGA tuned for that application)

>
> More or less RAC is the beast formerly know as a parallel server. You
> are assuming right about disk devices. However, all nodes must see the
> same datafiles, so node 1 & node 2 & node 3 must see at least X. The
> storage config is the same for all nodes on RAC.
> Instead of raw devices you can also use a certified clustered
> filesystem.
>

I haven't been following this thread, so apologies if this is off-topic, but I wanted to point out that this last paragraph does what a lot of people do, which is to confuse Oracle RAC (which is simply multiple-instances-one-database) with hardware clustering (which is, in this context at least, multiple-nodes-shared-storage).

It is perfectly legitimate to "partition" a hardware cluster so that different bits of it see different disks. Whether that's actually do-able in the first place depends entirely on the clustering hardware and topology chosen.

Where your sentence reads 'node 1, node 2 and node 3 must see at least disk group X', that is therefore not generically true. It is only true if, on those nodes, there are instances which seek to manage the same database which happens to be stored on disk group X.

I also don't understand what "the storage config is the same for all nodes on RAC", either. I think it falls into the same category of wobbly distinction between RACing and Clustering.

Regards
HJR Received on Mon Oct 04 2004 - 15:47:42 CDT