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 --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
  ]]