[linux-block.git] / Documentation / device-mapper / delay.rst

========
dm-delay
========

Device-Mapper's "delay" target delays reads and/or writes
and maps them to different devices.

Parameters::

    <device> <offset> <delay> [<write_device> <write_offset> <write_delay>
			       [<flush_device> <flush_offset> <flush_delay>]]

With separate write parameters, the first set is only used for reads.
Offsets are specified in sectors.
Delays are specified in milliseconds.

Example scripts
===============

::

	#!/bin/sh
	# Create device delaying rw operation for 500ms
	echo "0 `blockdev --getsz $1` delay $1 0 500" | dmsetup create delayed

::

	#!/bin/sh
	# Create device delaying only write operation for 500ms and
	# splitting reads and writes to different devices $1 $2
	echo "0 `blockdev --getsz $1` delay $1 0 0 $2 0 500" | dmsetup create delayed
Commit	Line	Data
	1	========
	2	dm-delay
	3	========
	4
	5	Device-Mapper's "delay" target delays reads and/or writes
	6	and maps them to different devices.
	7
	8	Parameters::
	9
	10	<device> <offset> <delay> [<write_device> <write_offset> <write_delay>
	11	[<flush_device> <flush_offset> <flush_delay>]]
	12
	13	With separate write parameters, the first set is only used for reads.
	14	Offsets are specified in sectors.
	15	Delays are specified in milliseconds.
	16
	17	Example scripts
	18	===============
	19
	20	::
	21
	22	#!/bin/sh
	23	# Create device delaying rw operation for 500ms
	24	echo "0 `blockdev --getsz $1` delay $1 0 500" \| dmsetup create delayed
	25
	26	::
	27
	28	#!/bin/sh
	29	# Create device delaying only write operation for 500ms and
	30	# splitting reads and writes to different devices $1 $2
	31	echo "0 `blockdev --getsz $1` delay $1 0 0 $2 0 500" \| dmsetup create delayed