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Re: Multiple hosts - shared SAN - ASM ?

From: Billy <vslabs_at_onwe.co.za>
Date: 31 May 2005 22:41:59 -0700
Message-ID: <1117604519.518102.107750@o13g2000cwo.googlegroups.com>


Mark Bole wrote:

> While I'm not saying running 15 instances (presumbably for 15 databases)
> on one host is a great idea, the math here is faulty, and anyone with
> basic ability to use Unix tools and Oracle's OFA will most definitely
> NOT incur N times the overhead (either administrative or disk/memory)
> just because they have N small instances instead of one large one (where
> N is some small integer). Values of N equal to two or three are no big
> deal and can be easily justified in a number of situations.

Mark, simply put you now have 15 distinct TEMP space areas instead of a single shared TEMP space resource. Ditto for the SGA, UNDO/REDO space and so on.

A shared resource is *many* times more scalable than indvidual non-shared resources. Just how small will the SGAs be when dealing with 15 of them? Just how big is the risk to have parts of the SGA paged to disk?

Think of scalability in operating systems and databases. Shared and virutal memory. Shared pool. Shared i/o buffers. Etc. You do not scale by making things non-sharable. Just what the hell is RAC? Multiple databases/instances per platform? No - the EXACT opposite. Single database serviced by mutiple platforms running a single RAC instance per platform.

Not too mention on an admin basis having to deal with 15 sets of bdump, udump and cdump directories and their contents on a daily basis. And backups and what not...

Yes, a good sysadm/dba (Oracle/Unix) will be able to deal with that (they always do).. but nor will a good sysadm/dba ever propose such a configuration.

THERE IS NO VALID TECHNICAL REASON FOR RUNNING MULTIPLE INSTANCES ON A SINGLE PLATFORM. The only exceptions to this is when dealing with very high-end servers where you do physical machine partitioning or when you have a R&D platform.

And if anyone beg to differ, please do it with technical fact and not personal fiction. (yeah, I have had this "debate" more times than I care to remember and every friggen time I have to listen to bs that is devoid of any technical facts and merrits to prop up the argument for having multiple instances per platform).

--
Billy
Received on Wed Jun 01 2005 - 00:41:59 CDT

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