Joel, I stand corrected.
Regards, Luis --- On Mon, 2/9/09, Joel Becker <joel.bec...@oracle.com> wrote: From: Joel Becker <joel.bec...@oracle.com> Subject: Re: [Ocfs2-users] ASM over OCFS2 vs. Standard locally managed tablespaces To: "Luis Freitas" <lfreita...@yahoo.com> Cc: "<ocfs2-users@oss.oracle.com>" <ocfs2-users@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.bec...@oracle.com Phone: (650) 506-8127
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