RE: ASM on SAN
Date: Mon, 22 Feb 2010 11:28:07 -0500
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This is a very nice presentation from Nitin on ASM and clearly mentions using an AU of 4M and talks about the note that you mentioned. If ORACLE has now backtracked from this I can't say
Quote "For all 11g ASM/DB users, it best to create a disk group using 4 MB ASM AU size. Metalink Note 810484.1 covers this" - slide 15
- Rajendra Pande -----Original Message----- From: oracle-l-bounce_at_freelists.org [mailto:oracle-l-bounce_at_freelists.org] On Behalf Of Martin Bach Sent: Monday, February 22, 2010 11:18 AM To: greg_at_structureddata.org Cc: cshapi_at_gmail.com; oracle-l Subject: Re: ASM on SAN
great reply, I second your approach. May I ask a question about the below paragraph please:
On 02/21/2010 10:23 PM, Greg Rahn wrote:
> The other thing is that most of the storage engineers (people that
> design this stuff) or performance engineers (people that perf test it)
> will tell you there is a sweet spot for the LUN size and
> characteristics. This varies from array to array, but I would seek
> out this information. It usually has to do with things like which
> drives are on what controllers and primary vs secondary IO paths, etc.
I remember a MOS document "Note 810484.1 "Recommendation for 4MB ASM Allocation Unit (AU) size for Oracle 11g" which seems to have disappeared when I tried to look it up is recommending au_size > 1MB. I found reference to it under the exadata best practices but I wondered when you'd set the AU_SIZE to a non-default value.
Our system here isn't too large, 2.5 TB, disk groups ctrllog VRAID 1 for online redo logs and control files, DATA for data (VRAID 5) and FRA with VRAID 5 as well. All ASM LUNs are 250G and use external redundancy. Unfortunately there is a severe lack of spindles and I would have preferred VRAID 1 for DATA but my comments about IO performance and checksum'd writes weren't listened to.
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