dm-delay — The Linux Kernel 6.14.0-gnu-rt3-parabola1-1-rt documentation

# 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”