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Josef Bacik3407ef52011-03-24 13:54:24 +00001dm-flakey
2=========
3
Mike Snitzerb26f5e32011-08-02 12:32:05 +01004This 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.
Josef Bacik3407ef52011-03-24 13:54:24 +00007
8Starting from the time the table is loaded, the device is available for
Mike Snitzerb26f5e32011-08-02 12:32:05 +01009<up interval> seconds, then exhibits unreliable behaviour for <down
10interval> seconds, and then this cycle repeats.
Josef Bacik3407ef52011-03-24 13:54:24 +000011
Mike Snitzerb26f5e32011-08-02 12:32:05 +010012Also, 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:
Josef Bacik3407ef52011-03-24 13:54:24 +000022 <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.
Mike Snitzerb26f5e32011-08-02 12:32:05 +010027
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.
Mike Snitzera3998792011-08-02 12:32:06 +010035
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