The Essbase Kernel uses buffered I/O (input/output) by default, but direct I/O is available on the operating systems and file systems that Essbase supports, with the exception of Linux. See the Oracle Hyperion Enterprise Performance Management System Certification Matrix (http://www.oracle.com/technology/software/products/ias/files/fusion_certification.html).
Buffered I/O uses the file system buffer cache.
Direct I/O bypasses the file system buffer cache and is able to perform asynchronous, overlapped I/Os. The following benefits are provided:
If you set a database to use direct I/O, Essbase attempts to use direct I/O the next time the database is started. If direct I/O is not available on your platform when the database is started, Essbase uses buffered I/O, which is the default. However, Essbase will store the I/O access mode selection in the security file and attempts to use that I/O access mode each time the database is started.