iostat (''input/output statistics'') is a computer

system monitor A system monitor is a Computer hardware, hardware or software component used to monitor system resources and performance in a computer system. Among the management issues regarding use of system monitoring tools are resource usage and privacy. ...

tool used to collect and show

operating system An operating system (OS) is system software that manages computer hardware, software resources, and provides common services for computer programs. Time-sharing operating systems schedule tasks for efficient use of the system and may also in ...

storage Storage may refer to: Goods Containers * Dry cask storage, for storing high-level radioactive waste * Food storage * Intermodal container, cargo shipping * Storage tank Facilities * Garage (residential), a storage space normally used to store car ...

input and output statistics. It is often used to identify performance issues with storage devices, including local disks, or remote disks accessed over network file systems such as NFS. It can also be used to provide information about

terminal Terminal may refer to: Computing Hardware * Terminal (electronics), a device for joining electrical circuits together * Terminal (telecommunication), a device communicating over a line * Computer terminal, a set of primary input and output devic ...

(TTY) input and output, and also includes some basic CPU information.

Syntax and availability

iostat -x displays output where each line (row) gives numerical data for one device. The first column lists the device name, and subsequent columns show various statistics for that device. Columns include the average service time (''svc_t'', which includes not only the time a request is in the service queue, but also the seek time and transfer time), the average busy percentage (''%b'', essentially the proportion of time that the device is in use), and the percentage of time that the queue is not empty (''%w'', which means the proportion of time in which requests from the device have not yet been fulfilled). It is best to run iostat specifying a time interval in seconds (for example iostat -x 30) in order to see the results over time. This is because otherwise, the output will reflect the values over the entire timespan since the system was last

rebooted ''Rebooted'' is the third season of the computer-animated television series '' Ninjago: Masters of Spinjitzu'' (titled ''Ninjago'' from the eleventh season onward). The series was created by Michael Hegner and Tommy Andreasen. The season aired f ...

. The iostat tool is available on most

Unix Unix (; trademarked as UNIX) is a family of multitasking, multiuser computer operating systems that derive from the original AT&T Unix, whose development started in 1969 at the Bell Labs research center by Ken Thompson, Dennis Ritchie, and ot ...

and

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operating systems, such as

FreeBSD FreeBSD is a free and open-source Unix-like operating system descended from the Berkeley Software Distribution (BSD), which was based on Research Unix. The first version of FreeBSD was released in 1993. In 2005, FreeBSD was the most popular ...

macOS macOS (; previously OS X and originally Mac OS X) is a Unix operating system developed and marketed by Apple Inc. since 2001. It is the primary operating system for Apple's Mac computers. Within the market of desktop and lapt ...

(''com.apple.pkg.Core'' package),

Linux Linux ( or ) is a family of open-source Unix-like operating systems based on the Linux kernel, an operating system kernel first released on September 17, 1991, by Linus Torvalds. Linux is typically packaged as a Linux distribution, which ...

(

sysstat sysstat (''system statistics'') is a collection of performance monitoring tools for Linux. It is available on Unix and Unix-like operating systems. Software included in sysstat package: * sar Collect, report, or save system activity informat ...

package), and

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. The syntax and output of iostat often differs slightly between them.

Output of the command

Sun Microsystems Sun Microsystems, Inc. (Sun for short) was an American technology company that sold computers, computer components, software, and information technology services and created the Java programming language, the Solaris operating system, ZFS, the ...

stated that high values in the ''wait'' and ''svc_t'' fields suggest a lack of overall throughput in the system, indicating that "the system is overloaded with I/O operations". Consistently high values in the ''kr/s'', ''kw/s'', ''%w'' and ''%b'' fields also indicate "a possible I/O bottleneck". In versions of Solaris before Solaris 7, iostat can give misleading information in the ''wait'' field on

multiprocessor Multiprocessing is the use of two or more central processing units (CPUs) within a single computer system. The term also refers to the ability of a system to support more than one processor or the ability to allocate tasks between them. There ar ...

systems. This is because iostat can misinterpret one

processor Processor may refer to: Computing Hardware * Processor (computing) **Central processing unit (CPU), the hardware within a computer that executes a program *** Microprocessor, a central processing unit contained on a single integrated circuit (I ...

being in a state where it is waiting for I/O, as meaning that all processors in the system are having to wait. It is also advisable to disregard high values in the ''svc_t'' field for disks that have very low rates of activity (less than 5%). This is because the ''fsflush'' process can force up the average service time when synchronising data on disk with what is in memory. iostat does not display information about the individual volumes on each disk if a

volume manager In computer storage, logical volume management or LVM provides a method of allocating space on mass-storage devices that is more flexible than conventional partitioning schemes to store volumes. In particular, a volume manager can concatenate, ...

is used . The ''vxstat'' command can be used to show this information instead. In contrast, when using Linux LVM as a volume manager, iostat does display volume information individually, because each logical volume has its own

device mapper The device mapper is a framework provided by the Linux kernel for mapping physical block devices onto higher-level ''virtual block devices''. It forms the foundation of the logical volume manager (LVM), software RAIDs and dm-crypt disk encryption, ...

(dm) device.

References

{{Reflist

External links

FreeBSD iostat(8) manual page

Mac OS X iostat manual page
Unix file system-related software System monitors Computer performance System administration

Syntax and availability

Output of the command

See also

References

External links