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Oracle Veritas vxfs filesystem optimization

Oracle Database Tips by Donald Burleson

When using Oracle Disk Manager with Veritas vxfs, what should be the proper setting for filesystem mount options (and file system io options), disk_async_io, convosync and DBWR processes?

Answer:  Every system has different optimizations, but here are some guidelines for optimizing Veritas vxfs on Oracle.  The Veritas Cluster Server, supporting Oracle RAC, is pretty much an extended and enhanced version of the VCS used for database failover clusters. Veritas DBE/AC is a certified cluster framework that is built in with Cluster File System and it is ODM compliant.

Set direct I/O for Veritas: convosync=direct.  It is also possible to enable direct I/O on a per-file basis using Veritas QIO; refer to the "qiostat" command and corresponding man page for hints.

Oracle's DBWR now writes continuously without waiting for previous writes to complete.  The new design allows DBWR to act as if it were inherently synchronous, regardless of whether the operating system supports asynchronous I/O or not. 

To determine whether to use multiple DBWn processes or database slaves, follow these guidelines:

  • Use db_writer_processes for most write intensive applications.  One per CPU is the recommended setting. 

  • Use db_writer_processes for databases that have a large data buffer cache.

  • Use dbwr_io_slaves for applications that are not write intensive and run on operating systems that support asynchronous I/O.

  • Use dbwr_io_slaves on platforms that do no support asynchronous I/O.

  • Use dbwr_io_slaves on single CPU systems.  Multiple DBWR processes are CPU intensive.

If you like Oracle tuning, you may enjoy the new book "Oracle Tuning: The Definitive Reference", over 900 pages of BC's favorite tuning tips & scripts. 

You can buy it direct from the publisher for 30%-off and get instant access to the code depot of Oracle tuning scripts.



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Note: This Oracle documentation was created as a support and Oracle training reference for use by our DBA performance tuning consulting professionals.  Feel free to ask questions on our Oracle forum.

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