IOSTAT(8)

NAME
iostat - report I/O statistics

SYNOPSIS
iostat [-CdhKIoT] [-c count] [-n devs] [ -t type,if,pass] [-w wait] [drives]

DESCRIPTION
Iostat displays kernel I/O statistics on terminal, device and cpu operations.

The options are as follows:

-c  Repeat the display count times. If no wait interval is specified, the default is 1 second.

-C  Display CPU statistics. This is on by default, unless -d is specified.

-d  Display only device statistics. If this flag is turned on, only device statistics will be displayed, unless -C or -T is also specified to enable the display of CPU or TTY statistics.

-D  Display more details. If this flag is turned on, details on read and write statistics will be displayed as MBw/s (Megabyte written per second), MBr/s (Megabyte read per second), rtps (read transactions per second) and wtps (write transactions per second).

-h  Put iostat in ‘top’ mode. In this mode, iostat will show devices in order from highest to lowest bytes per measurement cycle.

-I  Display total statistics for a given time period, rather than average statistics for each second during that time period.

-K  In the blocks transferred display (-o), display block count in kilobytes rather then the device native block size.

-n  Display up to devs number of devices. iostat will display fewer devices if there aren't devs devices present.

-o  Display old-style iostat device statistics. Sectors per second, transfers per second, and milliseconds per seek are displayed. If -I is specified, total blocks/sectors, total transfers, and milliseconds per seek are displayed.

-t  Specify which types of devices to display. There are three different categories of devices:

    device type:
        da  Direct Access devices
        sa  Sequential Access devices
        printer
            Printers
        proc
            Processor devices
        worm
            Write Once Read Multiple devices
        cd  CD devices
        scanner
            Scanner devices
        optical
            Optical Memory devices
        changer
            Medium Changer devices
        comm
            Communication devices
        array
            Storage Array devices
        enclosure
            Enclosure Services devices
        floppy
            Floppy devices

    interface:
        IDE Integrated Drive Electronics devices
        SCSI
            Small Computer System Interface devices
        other
            Any other device interface

    passthrough:
        pass
            Passthrough devices

    The user must specify at least one device type, and may specify at most one device type from each category. Multiple device types in a single device type statement must be separated by commas.

    Any number of -t arguments may be specified on the command line. All -t arguments are ORed together to form a matching expression against which all devices in the system are compared. Any device that fully matches any -t argument will be included in the iostat output, up to the number of devices that can be displayed in available columns (80 minimum), or the maximum number of devices specified by the user.

-T  Display TTY statistics. This is on by default, unless -d is specified.

-w  Pause wait seconds between each display. If no repeat count is specified, the default is infinity.

Iostat displays its information in the following format:

tty
    tin characters read from terminals
    tout
        characters written to terminals

devices
    Device operations. The header of the field is the device name and unit number. iostat will display as many devices as will fit in available columns (80 minimum), or the maximum number of devices in the system, whichever is smaller. If -n is specified on the command line, iostat will display the smaller of the requested number of devices, and the maximum number of devices in the system. To force iostat to display specific drives, their names may be supplied on the command line. iostat will not display more devices than will fit in available columns (80 columns minimum), unless the -n argument is given on the command line to specify a maximum number of devices to display. Fewer devices may be displayed.

    The standard iostat device display shows the following statistics:

    KB/t
        kilobytes per transfer
    tps transfers per second
    MB/s
        megabytes per second

    The standard iostat device display, with the -I flag specified, shows the following statistics:

    KB/t
        kilobytes per transfer
    xfrs
        total number of transfers
    MB  total number of megabytes transferred

    The old-style iostat display (using -o) shows the following statistics:

    sps sectors transferred per second
    tps transfers per second
    msps
        average milliseconds per transaction

    The old-style iostat display, with the -I flag specified, shows the following statistics:

    blk total blocks/sectors transferred
    xfr total transfers
    msps
        average milliseconds per transaction

cpu
    us  % of cpu time in user mode
    ni  % of cpu time in user mode running niced processes
    sy  % of cpu time in system mode
    in  % of cpu time in interrupt mode
    id  % of cpu time in idle mode

EXAMPLES
    iostat -w 1 da0 da1 cd0

Display statistics for the first two Direct Access devices and the first CDROM device every second ad infinitum.

    iostat -c 2

Display the statistics for the first four devices in the system twice, with a one second display interval.

    iostat -t da -t cd -w 1

Display statistics for all CDROM and Direct Access devices every second ad infinitum.

    iostat -t da,scsi,pass -t cd,scsi,pass

Display statistics once for all SCSI passthrough devices that provide access to either Direct Access or CDROM devices.

    iostat -h -n 8 -w 1

Display up to 8 devices with the most I/O every second ad infinitum.

    iostat -dh -t da -w 1

Omit the TTY and CPU displays, show devices in order of performance and show only Direct Access devices every second ad infinitum.

    iostat -Iw 3

Display total statistics every three seconds ad infinitum.

    iostat -odICTw 2 -c 9

Display total statistics using the old-style output format 9 times, with a two second interval between each measurement/display. The -d flag generally disables the TTY and CPU displays, but since the -T and -C flags are given, the TTY and CPU displays will be displayed.

SEE ALSO
fstat(1), netstat(1), nfsstat(1), ps(1), systat(1), pstat(8), vmstat(8)

The sections starting with ``Interpreting system activity'' in

HISTORY
This version of iostat first appeared in FreeBSD 3.0.

AUTHORS
Kenneth Merry <ken@FreeBSD.org>