A good thing to remember is that the top cause of slow performance of any Oracle database is disk I/O. Essentially, any Oracle database is a repository for data, and retrieving data from disk is a very expensive and time-consuming operation.
Because of the high amount of I/O that many Oracle systems experience, many Oracle professionals may consider the use of "raw" devices in conjunction with large block sizes (DB_BLOCK_SIZE). A raw device is a disk that bypasses the I/O overhead created by the Journal File System (JFS) in UNIX.
The reduction in disk I/O overhead can improve throughput, but only in cases where I/O is already the bottleneck for the Oracle database. Furthermore, raw devices require a tremendous amount of manual work for both the Oracle administrator and the systems administrator.
It's critical to know that Oracle recommends considering the use of raw devices only when the Oracle database is I/O bound. For these types of Oracle databases, raw devices can dramatically improve overall performance. But if the database is not I/O bound, switching to raw devices will have no impact on performance.
It's worth mentioning the feature in Oracle 8.1.7 called Direct I/O, which is supported on some of the top UNIX platforms. Veritas also sells a product called Quick I/O. These options give Oracle near raw performance without the additional overhead in managing raw devices.
Donald Burleson has been a database administrator for 23 years and has written 14 database books and over 100 articles. He is editor in chief of Oracle Internals and runs Burleson Oracle Consulting.