[linux-2.6-block.git] / Documentation / device-mapper / delay.txt

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>]

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 --getsize $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 --getsize $1` delay $1 0 0 $2 0 500" | dmsetup create delayed
]]
Commit	Line	Data
26b9f228 HM	1	dm-delay
	2	========
	3
	4	Device-Mapper's "delay" target delays reads and/or writes
	5	and maps them to different devices.
	6
	7	Parameters:
	8	<device> <offset> <delay> [<write_device> <write_offset> <write_delay>]
	9
	10	With separate write parameters, the first set is only used for reads.
f49e869a	11	Offsets are specified in sectors.
26b9f228 HM	12	Delays are specified in milliseconds.
	13
	14	Example scripts
	15	===============
	16	[[
	17	#!/bin/sh
	18	# Create device delaying rw operation for 500ms
	19	echo "0 `blockdev --getsize $1` delay $1 0 500" \| dmsetup create delayed
	20	]]
	21
	22	[[
	23	#!/bin/sh
	24	# Create device delaying only write operation for 500ms and
	25	# splitting reads and writes to different devices $1 $2
	26	echo "0 `blockdev --getsize $1` delay $1 0 0 $2 0 500" \| dmsetup create delayed
	27	]]