Re: Linux buffer cache monitoring

  • From: dba1 mcc <mccdba1@xxxxxxxxx>
  • To: Brandon.Allen@xxxxxxxxxxx,
  • Date: Wed, 3 Sep 2008 08:19:28 -0700 (PDT)

Don't use RAW device if possible.  Raw device depress on LINUX 5 and will 
desupport on LINUX 6.

--- On Wed, 9/3/08, Christo Kutrovsky <> wrote:

From: Christo Kutrovsky <>
Subject: Re: Linux buffer cache monitoring
To: Brandon.Allen@xxxxxxxxxxx
Cc: "Henry Poras" <henry@xxxxxxxxxxxxxxx>, "oracle-l" <oracle-l@xxxxxxxxxxxxx>
Date: Wednesday, September 3, 2008, 10:51 AM


Raw devices are just as easy to setup in virtual environments as file
systems. It's just a LUN without a filesystem created on it.

You may have to setup /dev/raw mappings, because block access devices
are also cached in linux unless you open them with direct IO flag. But
if you can open block devices like that, you should be able to open a
file as well.

You can also create "virtual" raw devices with files on the
filesystem, but I haven't checked whether those will be cached or not.

DirectIO is your best bet.

why not test directly from Oracle? Just do a index lookup in a loop
with several sessions.

On Fri, Jul 25, 2008 at 4:21 PM, Allen, Brandon
<Brandon.Allen@xxxxxxxxxxx> wrote:
> Hi Henry,
> I've never used Direct I/O on Linux, but I'll look into it.  I
don't see
> any options with the Orion utility to force it to use direct I/O, but
> maybe there is a filesystem mount option I can use to force it similar
> to the cio mount option on AIX.
> I considered using raw devices to test too, but my sysadmin is telling
> me that is difficult/impossible to setup because this is actually a
> virtual environment, running on top of Win2K8 HyperV, which is one
> reason why I want to make sure we're getting sufficient IO throughput.
> Thanks,
> Brandon
> -----Original Message-----
> From: Henry Poras [mailto:henry@xxxxxxxxxxxxxxx]
> I forget if it can be used with
> Direct I/O.
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Christo Kutrovsky
DBA Team Lead
The Pythian Group -
I blog at


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