1 dm-dust
2 =======
3
4 This target emulates the behavior of bad secto
5 locations, and the ability to enable the emula
6 at an arbitrary time.
7
8 This target behaves similarly to a linear targ
9 the user can send a message to the target to s
10 requests on specific blocks (to emulate the be
11 drive with bad sectors).
12
13 When the failure behavior is enabled (i.e.: wh
14 "dmsetup status" displays "fail_read_on_bad_bl
15 in the "bad block list" will fail with EIO ("I
16
17 Writes of blocks in the "bad block list will r
18
19 1. Remove the block from the "bad block list".
20 2. Successfully complete the write.
21
22 This emulates the "remapped sector" behavior o
23 sectors.
24
25 Normally, a drive that is encountering bad sec
26 encounter more bad sectors, at an unknown time
27 With dm-dust, the user can use the "addbadbloc
28 messages to add arbitrary bad blocks at new lo
29 "enable" and "disable" messages to modulate th
30 configured "bad blocks" will be treated as bad
31 This allows the pre-writing of test data and m
32 simulating a "failure" event where bad sectors
33
34 Table parameters
35 ----------------
36 <device_path> <offset> <blksz>
37
38 Mandatory parameters:
39 <device_path>:
40 Path to the block device.
41
42 <offset>:
43 Offset to data area from start of devi
44
45 <blksz>:
46 Block size in bytes
47
48 (minimum 512, maximum 1073741824,
49
50 Usage instructions
51 ------------------
52
53 First, find the size (in 512-byte sectors) of
54
55 $ sudo blockdev --getsz /dev/vdb1
56 33552384
57
58 Create the dm-dust device:
59 (For a device with a block size of 512 bytes)
60
61 ::
62
63 $ sudo dmsetup create dust1 --table '0
64
65 (For a device with a block size of 4096 bytes)
66
67 ::
68
69 $ sudo dmsetup create dust1 --table '0
70
71 Check the status of the read behavior ("bypass
72 will be passed through to the underlying devic
73 bad block additions, removals, and remaps will
74
75 $ sudo dmsetup status dust1
76 0 33552384 dust 252:17 bypass verbose
77
78 $ sudo dd if=/dev/mapper/dust1 of=/dev
79 128+0 records in
80 128+0 records out
81
82 $ sudo dd if=/dev/zero of=/dev/mapper/
83 128+0 records in
84 128+0 records out
85
86 Adding and removing bad blocks
87 ------------------------------
88
89 At any time (i.e.: whether the device has the
90 enabled or disabled), bad blocks may be added
91 device via the "addbadblock" and "removebadblo
92
93 $ sudo dmsetup message dust1 0 addbadb
94 kernel: device-mapper: dust: badblock
95
96 $ sudo dmsetup message dust1 0 addbadb
97 kernel: device-mapper: dust: badblock
98
99 $ sudo dmsetup message dust1 0 addbadb
100 kernel: device-mapper: dust: badblock
101
102 These bad blocks will be stored in the "bad bl
103 While the device is in "bypass" mode, reads an
104
105 $ sudo dmsetup status dust1
106 0 33552384 dust 252:17 bypass
107
108 Enabling block read failures
109 ----------------------------
110
111 To enable the "fail read on bad block" behavio
112
113 $ sudo dmsetup message dust1 0 enable
114 kernel: device-mapper: dust: enabling
115
116 $ sudo dmsetup status dust1
117 0 33552384 dust 252:17 fail_read_on_ba
118
119 With the device in "fail read on bad block" mo
120 block will encounter an "Input/output error"::
121
122 $ sudo dd if=/dev/mapper/dust1 of=/dev
123 dd: error reading '/dev/mapper/dust1':
124 0+0 records in
125 0+0 records out
126 0 bytes copied, 0.00040651 s, 0.0 kB/s
127
128 ...and writing to the bad blocks will remove t
129 therefore emulating the "remap" behavior of ha
130
131 $ sudo dd if=/dev/zero of=/dev/mapper/
132 128+0 records in
133 128+0 records out
134
135 kernel: device-mapper: dust: block 60
136 kernel: device-mapper: dust: block 67
137 kernel: device-mapper: dust: block 72
138 kernel: device-mapper: dust: block 87
139
140 Bad block add/remove error handling
141 -----------------------------------
142
143 Attempting to add a bad block that already exi
144 result in an "Invalid argument" error, as well
145
146 $ sudo dmsetup message dust1 0 addbadb
147 device-mapper: message ioctl on dust1
148 kernel: device-mapper: dust: block 88
149
150 Attempting to remove a bad block that doesn't
151 result in an "Invalid argument" error, as well
152
153 $ sudo dmsetup message dust1 0 removeb
154 device-mapper: message ioctl on dust1
155 kernel: device-mapper: dust: block 87
156
157 Counting the number of bad blocks in the bad b
158 ----------------------------------------------
159
160 To count the number of bad blocks configured i
161 following message command::
162
163 $ sudo dmsetup message dust1 0 countba
164
165 A message will print with the number of bad bl
166 configured on the device::
167
168 countbadblocks: 895 badblock(s) found
169
170 Querying for specific bad blocks
171 --------------------------------
172
173 To find out if a specific block is in the bad
174 following message command::
175
176 $ sudo dmsetup message dust1 0 querybl
177
178 The following message will print if the block
179
180 dust_query_block: block 72 found in ba
181
182 The following message will print if the block
183
184 dust_query_block: block 72 not found i
185
186 The "queryblock" message command will work in
187 and "disabled" modes, allowing the verificatio
188 will be treated as "bad" without having to iss
189 or having to "enable" the bad block emulation.
190
191 Clearing the bad block list
192 ---------------------------
193
194 To clear the bad block list (without needing t
195 a "removebadblock" message command for every b
196 following message command::
197
198 $ sudo dmsetup message dust1 0 clearba
199
200 After clearing the bad block list, the followi
201
202 dust_clear_badblocks: badblocks cleare
203
204 If there were no bad blocks to clear, the foll
205 appear::
206
207 dust_clear_badblocks: no badblocks fou
208
209 Listing the bad block list
210 --------------------------
211
212 To list all bad blocks in the bad block list (
213 with blocks 1 and 2 in the bad block list), ru
214 command::
215
216 $ sudo dmsetup message dust1 0 listbad
217 1
218 2
219
220 If there are no bad blocks in the bad block li
221 execute with no output::
222
223 $ sudo dmsetup message dust1 0 listbad
224
225 Message commands list
226 ---------------------
227
228 Below is a list of the messages that can be se
229
230 Operations on blocks (requires a <blknum> argu
231
232 addbadblock <blknum>
233 queryblock <blknum>
234 removebadblock <blknum>
235
236 ...where <blknum> is a block number within ran
237 (corresponding to the block size of the device
238
239 Single argument message commands::
240
241 countbadblocks
242 clearbadblocks
243 listbadblocks
244 disable
245 enable
246 quiet
247
248 Device removal
249 --------------
250
251 When finished, remove the device via the "dmse
252
253 $ sudo dmsetup remove dust1
254
255 Quiet mode
256 ----------
257
258 On test runs with many bad blocks, it may be d
259 excessive logging (from bad blocks added, remo
260 This can be done by enabling "quiet mode" via
261
262 $ sudo dmsetup message dust1 0 quiet
263
264 This will suppress log messages from add / rem
265 operations. Log messages from "countbadblocks
266 message commands will still print in quiet mod
267
268 The status of quiet mode can be seen by runnin
269
270 $ sudo dmsetup status dust1
271 0 33552384 dust 252:17 fail_read_on_ba
272
273 To disable quiet mode, send the "quiet" messag
274
275 $ sudo dmsetup message dust1 0 quiet
276
277 $ sudo dmsetup status dust1
278 0 33552384 dust 252:17 fail_read_on_ba
279
280 (The presence of "verbose" indicates normal lo
281
282 "Why not...?"
283 -------------
284
285 scsi_debug has a "medium error" mode that can
286 specified sector (sector 0x1234, hardcoded in
287 it uses RAM for the persistent storage, which
288 the potential device size.
289
290 dm-flakey fails all I/O from all block locatio
291 frequency, and not a given point in time.
292
293 When a bad sector occurs on a hard disk drive,
294 are failed by the device, usually resulting in
295 ("I/O error") or ENODATA ("No data available")
296 the sector may succeed, and result in the sect
297 after the device controller no longer experien
298 sector (or after a reallocation of the sector)
299 be bad sectors that occur on the device in the
300 unpredictable location.
301
302 This target seeks to provide a device that can
303 of a bad sector at a known sector location, at
304 on a large storage device (at least tens of gi
305 system memory).
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