Re: switch from file system to raw device

From: Igor <igor.news_at_merkudelete.org>
Date: Thu, 16 Sep 2004 13:54:53 +0200
Message-ID: <pan.2004.09.16.11.54.51.933920@merkudelete.org>

On Wed, 15 Sep 2004 15:24:54 +0200, Anton Dischner wrote:

> Hi Igor,
>
> i did some Oracle on AIX with Oracle 6.x and 7.x in 1992-1995.
>
> I had the official statement from IBM that raw devices with this
> configuration is -slower- than filesystem use.
Another thing about "official statements", Anton, please allow.

Of course, we did not just test things, but talked to people and read documentation. In fact, people do not have much familiarity with raw device, as Hans stated, too. On the other hand, there is an Reference Addendum to 7.3.4 on AIX, which tries not to convince you of either way to chose, but tries to just number issues you might or should have in mind when discussing about raw devices.
Among other things they write

- I/O is done directly from the disk to the SGA with little CPU overhead
- overhead of OS read ahead is avoided
- OS file system overhead is avoided
- OS cache and Oracle buffer cache are independently tuned
- reduced OS buffer cache size frees mem for other uses

Among the disadvantages numbered in this chapter we found nothing that convinced us not to go into raw device.
But this is just a note to say, we didn't go on raw device just because it "sounds better", even if you surely didn't want to make this kind of comment.

Thanks a lot for contributing.
Have a nice day,
Igor Received on Thu Sep 16 2004 - 06:54:53 CDT