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RE: Fencing Cache in Disk Array for Oracle

From: Binh Pham <>
Date: Wed, 8 Aug 2007 09:03:09 -0700
Message-ID: <BAY103-DAV147BD321B0A4284E309717D2E70@phx.gbl>
Message-ID: <01bd01c7d9d5$9d5c45c0$>

Even though I’m planning to work with the Storage Administrator to monitor the hit ratio and adjust it accordingly, however, I’m just trying to find a reasonable number to start with and I want to back up this initial number with some reasonable backup facts.  


From: [] On Behalf Of Allan Nelson
Sent: Wednesday, August 08, 2007 5:37 AM To: oracle-l
Subject: Re: Fencing Cache in Disk Array for Oracle  

The cache he is talking about is in the array and hence is not available to the SGA. I fear that you are in for some iteration. The amount of usable cache memory depends on the unique I/O signature of your database. With this particular array, and assuming you have 2Gb fibre you should expect reads and writes always down in single digit ms area. Tune with your choice of tool until you are as close to this as possible.


On 8/5/07, LS Cheng <> wrote:

one of opinions here:  

MySql focused but applies to any database vendor  



LSC   On 8/4/07, Binh Pham < > wrote:

I'm currently working on a project that involves a new HP XP12000 Disk Array. The newly acquired array would have 240G of cache on the array that allows data to be cached between the physical disks and the servers. This model allows an amount of cache to be dedicated (fenced) to a specific host, in this case, the production server therefore other non-production related activities can pollute the production cache. The rest of the cache can be shared among the rest of the non-production servers.  

My question is that how much cache should be allocated to ensure top performance in terms of IO for the production server? I'm not comfortable with throwing out a number and say that it is good. What I'm looking for is some researchable facts that back up the number (for example, something that I can mine from statspacks or similar that can be used to determine this number).  

Thanks for any input.  

Binh Pham  

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-- Received on Wed Aug 08 2007 - 11:03:09 CDT

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