[Ocfs2-users] ocfs Vs ocfs2

[Joel Becker]

On Tue, Jan 16, 2007 at 01:28:41AM -0800, GOKHAN wrote:
> Hi everbody this is my first post,
> I have two test server .(Both of them is idle)
> db1 : RHEL4 OCFS2
> db2 : RHEL3 OCFS
> 
> I test the IO both of them
> The result is below.
> 
>  db1(Time Spend)db2(Time Spend)OS Test Command
> dd (1GB) (Yazma)0m0.796s0m18.420stime dd if=/dev/zero of=./sill.t bs=1M count=1000
> dd (1GB) (Okuma)0m0.241s8m16.406stime dd of=/dev/zero if=./sill.t bs=1M count=1000
> cp (1GB)0m0.986s7m32.452stime cp sill.t sill2.t

	You are using dd(1), which does not use O_DIRECT.  The original
ocfs (on 2.4 kernels) does not really support buffered I/O well.  What
you are seeing is ocfs2 taking much better care of your buffered I/Os.
They will be consistent across the cluster.  In the ocfs case, you are
caching a lot more because these safety precautions aren't taken.
	HOWEVER, the most important factor is that you are not using
O_DIRECT.  When you actually run the database, you _will_ be using
O_DIRECT (make sure to mount ocfs2 with '-o datavolume').  Without the
OS caching in the way, both filesystems should run at the same speed.
	The upshot is that buffered I/O operations (such as plain dd(1))
are often not good indicators of database speed.

Joel

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Joel Becker
Principal Software Developer
Oracle
E-mail: joel.becker at oracle.com
Phone: (650) 506-8127