RE: Fencing Cache in Disk Array for Oracle

  • From: "Binh Pham" <binhpham15@xxxxxxxxxxx>
  • To: <anelson77388@xxxxxxxxx>, "'oracle-l'" <oracle-l@xxxxxxxxxxxxx>
  • Date: Wed, 8 Aug 2007 09:03:09 -0700

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: oracle-l-bounce@xxxxxxxxxxxxx [mailto:oracle-l-bounce@xxxxxxxxxxxxx]
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 <exriscer@xxxxxxxxx> wrote:

one of opinions here: 


MySql focused but applies to any database vendor







On 8/4/07, Binh Pham <binhpham15@xxxxxxxxxxx > 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
Thanks for any input.
Binh Pham



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