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Donald K. Burleson

Oracle RAC Tips

HP Tru64 CFS

Tru64 CFS is a layer on top of the Advfs file system. When direct I/O is enabled for a file by opening the file with the o_directio flag, read and write requests on it are executed to and from disk storage through direct memory access, bypassing AdvFS and CFS caching. This improves I/O performance for database applications that do their own caching and file region synchronization.

Oracle uses the direct I/O feature available in CFS. Direct I/O enables Oracle to bypass the buffer cache (no caching at file system level). Oracle manages the concurrent access to the file itself as it does on raw devices. Direct I/O does not go through the CFS server. File creation and resizing is seen as a metadata operation by Advfs and this has to be done by the CFS server. Consequently, file creations and resizes must be run on the node where the CFS server is located. File operations might take longer when the CFS server is remote.

In a TruCluster server, the device request dispatcher subsystem controls all I/O to physical devices. All cluster I/O passes through this subsystem, which enforces single-system open semantics so only one program can open a device at any one time.

General Features of a Tru64 CFS

  • The Cluster File System (CFS) makes all files, including the root (/), /usr, and/var file systems, visible to and accessible by all cluster members. There is a single copy or image for all cluster members.
  • A single cluster member serves each file system. Other members access that file system as CFS clients, with significant optimization for shared access.
  • Oracle9i RAC automatically does direct I/O on Tru64 UNIX file system storage. This can significantly improve I/O performance for the database since Oracle9i does its own caching and file region synchronization.

For more information, see the book Oracle 11g Grid and Real Application Clusters 30% off if you buy it directly from Rampant TechPress . 

Written by top Oracle experts, this RAC book has a complete online code depot with ready to use RAC scripts.





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