iotail(1M)                                                       iotail(1M)

NAME
     iotail - IO request statistics monitor

SYNOPSIS
     iotail [-ynptvADO] [-m num] [device]

DESCRIPTION
     iotail continuously prints the service times (in micro-seconds) of IO
     requests as they are completed for a single device. Typically, this
     information is used to produce graphs describing the performance
     characteristics of an IO subsystem or to follow the device usage pat-
     tern of an application.

     Any number of iotail commands can be simultaneously active on a system
     for any combination of traceable devices. This includes several invo-
     cations of iotail tracing the same device.

     By default, iotail will display requests as:

          ssssssss + dddddddd = tttttttt C  llllllll OOOOOOOO

     Where:

     ssssssss  is the length of time the request remained queued in the
               device driver before it was passed on to the device.

     dddddddd  is the length of time the device took to complete the
               request.

     tttttttt  is the sum of ssssssss and dddddddd.

     C         is R if it was a read or receive request and is W if it was
               a write or send request.

     llllllll  is the length of the request in bytes.

     OOOOOOOO  is device-specific information that may be present for some
               types of devices. For disks the format of this information
               is as follows:

                    [cccc:hhhh:ssss]

               Where:

               cccc      is the cylinder number.

               hhhh      is the head or track number.

               ssss      is the sector.

OPTIONS
     -y        turns on request tracing for device.



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iotail(1M)                                                       iotail(1M)

     -n        turns off request tracing for device.

     -p        continuously displays traced requests for device.

     -t        prints a table of traceable devices.

     -v        is verbose when printing traceable devices using -t.

     -m num    For efficiency, iotail waits until num requests have
               occurred before displaying them. The default is 5 requests.

     -A        prints absolute time values (in micro-seconds) relative to
               an arbitrary zero point. The times displayed are:

               start       when the kernel device driver receives the
                           request.

               devstart    when the request is sent to the device.

               done        when the request completes or the system
                           receives the completion interrupt.

     -D        prints on each line the difference between the completion
               time of the request on the previous line and the device
               start time of the request on the current line.

     -O        Displays the device specific opaque data numerically.

SEE ALSO
     dkstat(1M).
























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