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Documentation / device-mapper / dm-flakey.txt




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Based on kernel version 3.13. Page generated on 2014-01-20 22:00 EST.

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
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