Re: ASM on SAN

From: Greg Rahn <greg_at_structureddata.org>
Date: Tue, 23 Feb 2010 07:37:28 -0800
Message-ID: <a9c093441002230737t1c54270dr132f4b46fe4515bd_at_mail.gmail.com>

The reason for that recommendation was due to bug 7436152 (in 11.1.0.7) and there is a one off patch for it now and it is fixed in 11.2.

On Tue, Feb 23, 2010 at 1:02 AM, Luca Canali <Luca.Canali_at_cern.ch> wrote:
> BTW, MOS Note 759429.1 recommends "Disable ASM Variable sized extents if using a 4MB AU size and files will exceed 80G", there is also a short explanation in the note. While this seems to apply to 11.1.0.7, I wonder if it is also the case for 11.2 and for "non-exadata" DBs too.
>
> Cheers,
> L.
>
> -----Original Message-----
> From: oracle-l-bounce_at_freelists.org [mailto:oracle-l-bounce_at_freelists.org] On Behalf Of Greg Rahn
> Sent: 23 February 2010 00:21
> To: Martin Bach
> Cc: cshapi_at_gmail.com; oracle-l
> Subject: Re: ASM on SAN
>
> The default in 11g for AU_SIZE is still 1MB, and with Exadata it is
> set to 4MB.  The reason for this is that it places 4x as much data on
> a single ASM Disk (also called a Grid Disk with Exadata, which is
> really a partition of a physical disk) which results in more
> sequential read throughput.  In terms of sequential scan throughput,
> there is only modest gains after 4MB.
>
> As mentioned by some of the other responses AU_SIZE in 11g can be set
> to 1, 2, 4, 8, 16, 32, and 64 MB and it is also variable in size.  It
> is AU_SIZE for the first 20k extents, then 8*AU_SIZE for the next 20k
> extents, then 64*AU_SIZE for the next 20k, etc.
> ( see http://download.oracle.com/docs/cd/B28359_01/server.111/b31107/asmcon.htm#BABCGDBF
> )
> One of the reasons for this was to reduce the metadata sizes as the
> number of extents get larger.
>
> On Mon, Feb 22, 2010 at 8:17 AM, Martin Bach
> <development_at_the-playground.de> wrote:
>> 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.
>
>
> --
> Regards,
> Greg Rahn
> http://structureddata.org
> --
> http://www.freelists.org/webpage/oracle-l
>
>
>

-- 
Regards,
Greg Rahn
http://structureddata.org
--
http://www.freelists.org/webpage/oracle-l

Received on Tue Feb 23 2010 - 09:37:28 CST