Re: Multiple hosts - shared SAN - ASM ?

From: Mark Bole <makbo_at_pacbell.net>
Date: Tue, 31 May 2005 16:56:15 GMT
Message-ID: <PG0ne.637$IE7.241@newssvr21.news.prodigy.com>

DA Morgan wrote:

> Billy wrote:
> 

>> josodijk2_at_gmail.com wrote:
>>
>>
>>> We're about to replace 20 Unix systems. New hardware includes a SAN.
>>> Upgrading to Oracle 10G (mostly 1, but 1 host might have 15 instances)
>>> is part of the project. None will have 'high performance' requirements.
>>> Database sizes are in the 10 - 50 GB range. Ease of admin (both at the
>>> DBA and at the SA level) is important.
>>>
>>> Is ASM a good thing in this environment?
>>
>>
>>
>> Who cares!?
>>
>> After all, the plan is to run 15 instances on one host.. which means 15
>> times the admin requirements on that host, 15 times the problems, 15
>> times TEMP/REDO/ARCHIVELOG/etc space requirements, 15 times the
>> footprint of an Oracle instance ito DBWR, LOGWR, PMON, SMON and so on..
>>
>> Come one.. ASM or not ASM does not matter at all in such environment.
>> It is already shot to hell admin and performance wise.
>>
>> --
>> Billy

> 
> 
> True. I wasn't focusing on that part. But true. Hopefully the OP didn't
> mean what was actually written.

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.

On the other hand, even with one database per host, to use ASM in this scenario will require double the number of instances (one for the database, one for ASM) on each host, and if best practices are followed,   double the number of ORACLE_HOMEs.

So, like any such decision, you have to weigh the trade-offs. Having twenty ASM instances from twenty nodes all hooked up to one SAN might be more administrative overhead than you care to handle, especially if your current practices involve managing various types of database files (such as archived redo logs) at the Unix level, since the only way to get any files in or out of ASM is to use RMAN (in other words, your SA will most likely be out of the picture at this point, which could be good or bad, depending on your organization).

Fortunately, you can migrate to and from ASM (see various notes on Metalink) so you don't have to make an all-or-nothing decision up front.

-Mark Bole Received on Tue May 31 2005 - 11:56:15 CDT