Determining the Cause of Unusual Disk Latency

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LEARN ABOUT OSX

iotop

iotop(1m)							   USER COMMANDS							 iotop(1m)

NAME

       iotop - display top disk I/O events by process. Uses DTrace.

SYNOPSIS

       iotop [-C] [-D|-o|-P] [-j|-Z] [-d device] [-f filename] [-m mount_point] [-t top] [interval [count]]

DESCRIPTION

       iotop tracks disk I/O by process, and prints a summary report that is refreshed every interval.

       This is measuring disk events that have made it past system caches.

       Since this uses DTrace, only users with root privileges can run this command.

OPTIONS

       -C     don't clear the screen

       -D     print delta times - elapsed, us

       -j     print project ID

       -o     print disk delta times, us

       -P     print %I/O (disk delta times)

       -Z     print zone ID

       -d device
	      instance name to snoop (eg, dad0)

       -f filename
	      full pathname of file to snoop

       -m mount_point
	      mountpoint for filesystem to snoop

       -t top print top number only

EXAMPLES

       Default output, print summary every 5 seconds
	      # iotop

       One second samples,
	      # iotop 1

       print %I/O (time based),
	      # iotop -P

       Snoop events on the root filesystem only,
	      # iotop -m /

       Print top 20 lines only,
	      # iotop -t 20

       Print 12 x 5 second samples, scrolling,
	      # iotop -C 5 12

FIELDS

       UID    user ID

       PID    process ID

       PPID   parent process ID

       PROJ   project ID

       ZONE   zone ID

       CMD    command name for the process

       DEVICE device name

       MAJ    device major number

       MIN    device minor number

       D      direction, Read or Write

       BYTES  total size of operations, bytes

       ELAPSED
	      total elapsed times from request to completion, us (this is the elapsed time from the disk request (strategy) to the disk completion
	      (iodone))

       DISKTIME
	      total times for disk to complete request, us (this is the time for the disk to complete that  event  since  it's	last  event  (time
	      between iodones), or, the time to the strategy if the disk had been idle)

       %I/O   percent disk I/O, based on time (DISKTIME)

       load   1 minute load average

       disk_r total disk read Kb for sample

       disk_w total disk write Kb for sample

DOCUMENTATION

       See the DTraceToolkit for further documentation under the Docs directory. The DTraceToolkit docs may include full worked examples with ver-
       bose descriptions explaining the output.

EXIT

       iotop will run forever until Ctrl-C is hit, or the specified interval is reached.

AUTHOR

       Brendan Gregg [Sydney, Australia]

SEE ALSO

       iosnoop(1M), dtrace(1M)

version 0.75							   Oct 25, 2005 							 iotop(1m)

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