Oracle Database Administration: The Essential Refe

Disk layout

Oracle, like all relational databases, will probably be I/O bound. The second most important way to improve performance (after adding more memory) is to improve the overall performance of the I/O system. The more disks you can provide to Oracle, the better your I/O performance will be. Remember, for each table update you perform, Oracle will perform the following disk I/Os:

• The write to the table

• Updates to any indexes

• Rollback information for the table and indexes

• Redo log buffer writes to disk for the table and indexes

• Updates to the data dictionary if new extents are needed

For the best performance, follow these guidelines when you are laying out the disk subsystem:

• Allocate separate disks for data, redo logs, and archive files.

• Use multiple controllers when available.

• Use disk striping (either by the operating system or by Oracle).

• Keep data and index segments on separate disks for a given table.

• Use a separate disk for rollback segments.

• Keep the system tablespace on a separate disk or a lightly used disk.

• Avoid the use of RAID-5 disks (RAID stands for redundant arrays of inexpensive disks) for high-write files. Such files include rollback segments, temporary tablespaces, redo logs, and tables with high amounts of inserts, updates, and deletes. RAID-5 maintains data and parity information on multiple disks. The time spent reading, calculating, and writing to multiple disks will impact your total performance.

For more information about how Oracle uses disks and files, see Chapter ...