[Ocfs2-users] ASM over OCFS2 vs. Standard locally managed tablespaces

[Luis Freitas]

Joel,

  I stand corrected.

Regards,
Luis

--- On Mon, 2/9/09, Joel Becker <Joel.Becker at oracle.com> wrote:
From: Joel Becker <Joel.Becker at oracle.com>
Subject: Re: [Ocfs2-users] ASM over OCFS2 vs. Standard locally managed tablespaces
To: "Luis Freitas" <lfreitas34 at yahoo.com>
Cc: "<ocfs2-users at oss.oracle.com>" <ocfs2-users at oss.oracle.com>
Date: Monday, February 9, 2009, 3:25 PM

On Mon, Feb 09, 2009 at 04:16:23AM -0800, Luis Freitas wrote:
>    About the performance, ASM is said to have similar performance to raw
devices in a SAME layout, being tightly integrated to Oracle. OCFS2 has some
overheads that are inherent to a file system, like cache management, locking,
context switching, so it is likely to use more CPU power than ASM. But I dont
remember any specific benchmark comparing those. 

	ocfs2 has performance equivalent to raw devices when using
O_DIRECT, which the database will do for its datafiles.  We worked hard
at that from the beginning.  You won't see filesystem overhead for the
O_DIRECT access.  You only see the overhead of cache management, etc,
for cached (non-O_DIRECT) files, which isn't what you're worried about
for database performance.

>     Also, keep in mind that when you use a filesystem you are using
part of the memory for the filesystem cache. When using RAW or ASM you would
need to allocate this memory to the block buffer in order to compare results.

	Again, Oracle uses O_DIRECT for datafiles.  This keeps the data
out of the filesystem cache.  A single-node (non-RAC) database can use
the filesystem cache, and that can cause benchmark discrepancies, but
we're talking about RAC here.

Joel

-- 

To spot the expert, pick the one who predicts the job will take the
longest and cost the most.

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



      
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