Root/Documentation/device-mapper/dm-flakey.txt

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 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
48Examples:
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
54

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