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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