Re: Subject: RE: ASM - number of LUNS rule of thumb
- From: Jeremy Schneider <jeremy.schneider@xxxxxxxxxxxxxx>
- To: George Johnson <George.Johnson@xxxxxxx>, oracle-l digest users <oracle-l@xxxxxxxxxxxxx>
- Date: Thu, 19 Aug 2010 09:58:49 -0500
Sorry for the late response...
This is not true. All LUNs do not have to be the same size in ASM.
However, it is a best practice (and I have recommended it to people
before). Mainly because it's quite easy to mess things up with ASM and
storage if everything isn't the same in a diskgroup.
But the actual important thing is not size - it's that the underlying
storage is balanced. ASM stripes based on capacity. If two LUNS are
the same size but one uses 7200 rpm drives and the other uses 15000 rpm
drives, then this can cause difficult-do-diagnose performance oddities.
(Not to mention different RAID levels!!) But if two LUNS are different
sizes but both are RAID10 arrays of the exact same size/speed disks,
then actually ASM will handle it quite well and the data will end up
being spread evenly across all disk heads. There's storage network
pipes to think about too, but that's not usually an issue because a
single LUN typically is a small percentage of the traffic.
-Jeremy
David Robillard wrote:
> Hello George,
>
> One thing to keep in mind with ASM is that all LUNs in your disk
> groups must be of equal size.
> So if you use, say, 100 GB LUNs with ASM. Then when your database
> needs more storage, you'll need to add a 100 GB LUN to your disk
> group.
>
> There was an interesting presentation on ASM on
> http://www.oracleracsig.org. Do a search for %ASM% in the documents
> section of the site.
>
> HTH,
>
> David
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Jeremy Schneider
Chicago
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