linux/Documentation/device-mapper/dm-flakey.txt
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   1dm-flakey
   2=========
   3
   4This target is the same as the linear target except that it exhibits
   5unreliable behaviour periodically.  It's been found useful in simulating
   6failing devices for testing purposes.
   7
   8Starting from the time the table is loaded, the device is available for
   9<up interval> seconds, then exhibits unreliable behaviour for <down
  10interval> seconds, and then this cycle repeats.
  11
  12Also, consider using this in combination with the dm-delay target too,
  13which can delay reads and writes and/or send them to different
  14underlying devices.
  15
  16Table parameters
  17----------------
  18  <dev path> <offset> <up interval> <down interval> \
  19    [<num_features> [<feature arguments>]]
  20
  21Mandatory 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
  28Optional 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 s1oion>
  
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