NAME

iopending - plot number of pending disk events. Uses DTrace.

SYNOPSIS

iopending [-c] [-d device] [-f filename] [-m mount_point] [interval [count]]

DESCRIPTION

This samples the number of disk events that are pending and plots a distribution graph. By doing this the "serialness" or "parallelness" of disk behaviour can be distinguished. A high occurance of a pending value of more than 1 is an indication of saturation.

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

OPTIONS

-c: clear screen
-d device: instance name to snoop (eg, dad0)
-f filename: full pathname of file to snoop
-m mount_point: mountpoint for filesystem to snoop

EXAMPLES

Default output, print I/O summary every 1 second,: # iopending
Print 10 second samples,: # iopending 10
Print 12 x 5 second samples,: # iopending 5 12
Snoop events on the root filesystem only,: # iopending -m /

FIELDS

value: number of pending events, 0 == idle
count: number of samples @ 1000 Hz
load: 1 min load average
disk_r: total disk read Kb for sample
disk_w: total disk write Kb for sample

IDEA

Dr Rex di Bona

DOCUMENTATION

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

EXIT

iopending will run forever until Ctrl-C is hit, or the specified count is reached.

AUTHOR

Brendan Gregg [Sydney, Australia]