Documentation/device-mapper/dm-flakey.txt

   1 dm-flakey
   2 =========
   3
   4 This target is the same as the linear target except that it exhibits
   5 unreliable behaviour periodically.  It's been found useful in simulating
   6 failing devices for testing purposes.
   7
   8 Starting from the time the table is loaded, the device is available for
   9 <up interval> seconds, then exhibits unreliable behaviour for <down
  10 interval> seconds, and then this cycle repeats.
  11
  12 Also, consider using this in combination with the dm-delay target too,
  13 which can delay reads and writes and/or send them to different
  14 underlying devices.
  15
  16 Table parameters
  17 ----------------
  18   <dev path> <offset> <up interval> <down interval> \
  19     [<num_features> [<feature arguments>]]
  20
  21 Mandatory parameters:
  22     <dev path>: Full pathname to the underlying block-device, or a
  23                 "major:minor" device-number.
  24     <offset>: Starting sector within the device.
  25     <up interval>: Number of seconds device is available.
  26     <down interval>: Number of seconds device returns errors.
  27
  28 Optional feature parameters:
  29   If no feature parameters are present, during the periods of
  30   unreliability, all I/O returns errors.
  31
  32   drop_writes:
  33         All write I/O is silently ignored.
  34         Read I/O is handled correctly.
  35
  36   corrupt_bio_byte <Nth_byte> <direction> <value> <flags>:
  37         During <down interval>, replace <Nth_byte> of the data of
  38         each matching bio with <value>.
  39
  40     <Nth_byte>: The offset of the byte to replace.
  41                 Counting starts at 1, to replace the first byte.
  42     <direction>: Either 'r' to corrupt reads or 'w' to corrupt writes.
  43                  'w' is incompatible with drop_writes.
  44     <value>: The value (from 0-255) to write.
  45     <flags>: Perform the replacement only if bio->bi_rw has all the
  46              selected flags set.
  47
  48 Examples:
  49   corrupt_bio_byte 32 r 1 0
  50         - replaces the 32nd byte of READ bios with the value 1
  51
  52   corrupt_bio_byte 224 w 0 32
  53         - replaces the 224th byte of REQ_META (=32) bios with the value 0