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========
dm-delay
========
Device-Mapper's "delay" target delays reads and/or writes
and/or flushs and optionally maps them to different devices.
Arguments::
<device> <offset> <delay> [<write_device> <write_offset> <write_delay>
[<flush_device> <flush_offset> <flush_delay>]]
Table line has to either have 3, 6 or 9 arguments:
3: apply offset and delay to read, write and flush operations on device
6: apply offset and delay to device, also apply write_offset and write_delay
to write and flush operations on optionally different write_device with
optionally different sector offset
9: same as 6 arguments plus define flush_offset and flush_delay explicitely
on/with optionally different flush_device/flush_offset.
Offsets are specified in sectors.
Delays are specified in milliseconds.
Example scripts
===============
::
#!/bin/sh
#
# Create mapped device named "delayed" delaying read, write and flush operations for 500ms.
#
dmsetup create delayed --table "0 `blockdev --getsz $1` delay $1 0 500"
::
#!/bin/sh
#
# Create mapped device delaying write and flush operations for 400ms and
# splitting reads to device $1 but writes and flushs to different device $2
# to different offsets of 2048 and 4096 sectors respectively.
#
dmsetup create delayed --table "0 `blockdev --getsz $1` delay $1 2048 0 $2 4096 400"
::
#!/bin/sh
#
# Create mapped device delaying reads for 50ms, writes for 100ms and flushs for 333ms
# onto the same backing device at offset 0 sectors.
#
dmsetup create delayed --table "0 `blockdev --getsz $1` delay $1 0 50 $2 0 100 $1 0 333"
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