The iostat utility is a performance monitoring tool that is included with many Unix-based operating systems, including Linux and Solaris. It can be used to measure I/O (input/output) against physical disks in an Oracle database. Here's how to use iostat to measure I/O against physical disks in Oracle:
- Open a terminal window on the Oracle database server.
- Type "iostat -x" to run the iostat utility in extended mode. The "-x" option displays detailed disk I/O statistics, including the number of read and write operations, the number of kilobytes read and written, and the percentage of CPU time spent on I/O.
- Press Enter to execute the command.
- Monitor the output of iostat to see the I/O performance of the physical disks on the Oracle database server. Look for high values in the "rkB/s" and "wkB/s" columns, which indicate high disk I/O activity.
- Identify the physical disks that are experiencing high I/O activity by looking at the "Device" column. Note the device name, such as "sda" or "sdb".
- Use the Oracle Enterprise Manager (OEM) or the command-line tool "iostat" with the "-d" option to identify which Oracle database files are mapped to the high I/O physical disks. For example, you can type "iostat -d -x /dev/sda" to display I/O statistics for the physical disk "sda" and identify which database files are mapped to that disk.
- Use this information to optimize the I/O subsystem for the Oracle database. This may include adding more physical disks, configuring RAID, tuning the disk scheduler, or tuning the buffer cache.
In summary, the iostat utility can be used to measure I/O against physical disks in an Oracle database. By monitoring the I/O performance of physical disks and identifying the database files that are mapped to them, DBAs can optimize the I/O subsystem for the Oracle database and improve performance.