Re: ASM Question - Best Practice

From: K Gopalakrishnan <>
Date: Wed, 4 Jun 2008 09:05:03 -0700 (PDT)
Message-ID: <>


Good that you are asking the questions at planning phase (!),

> The intention is to use ASM. So first question: The mirroring can be
> done within ASM; i.e. by Oracle, or we can do it at the SAN level.
> Any advice or recommendations as to which is likely to be better?
> Availability and resilience will probably rank ahead of performance in
> terms of user requirements.

The choice is totally yours. If you think your SAN mirroring is better than ASM you can use SAN mirroring and choose the external redundancy to ASM. In short, ASM mirroring is done at the 'server' level and SAN mirroring is done at 'controller' level. So there may be some additional CPU overheads in ASM mirroring which may or may not be an issue.

However with ASM mirroring, you have the luxury of having many disk groups with different redundancy levels, like double or triple mirroring for system/data and no mirroring for temp tablespaces and so on. You can do the same at SAN level, but that is not as simple as you do in ASM.

Also you don't need to reserve a hot spare for ASM mirroring as ASM mirrors the 'extents' which are just 1M pieces of storage blocks (aka allocation units). This gives a better utilization of available disks, but doesn't matter these days!!

-Gopal Received on Wed Jun 04 2008 - 11:05:03 CDT

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