This allows the pre-writing of test data and metadata prior to
simulating a "failure" event where bad sectors start to appear.
-Table parameters:
------------------
+Table parameters
+----------------
<device_path> <offset> <blksz>
Mandatory parameters:
- <device_path>: path to the block device.
- <offset>: offset to data area from start of device_path
- <blksz>: block size in bytes
+ <device_path>:
+ Path to the block device.
+
+ <offset>:
+ Offset to data area from start of device_path
+
+ <blksz>:
+ Block size in bytes
+
(minimum 512, maximum 1073741824, must be a power of 2)
-Usage instructions:
--------------------
+Usage instructions
+------------------
-First, find the size (in 512-byte sectors) of the device to be used:
+First, find the size (in 512-byte sectors) of the device to be used::
-$ sudo blockdev --getsz /dev/vdb1
-33552384
+ $ sudo blockdev --getsz /dev/vdb1
+ 33552384
Create the dm-dust device:
(For a device with a block size of 512 bytes)
-$ sudo dmsetup create dust1 --table '0 33552384 dust /dev/vdb1 0 512'
+
+::
+
+ $ sudo dmsetup create dust1 --table '0 33552384 dust /dev/vdb1 0 512'
(For a device with a block size of 4096 bytes)
-$ sudo dmsetup create dust1 --table '0 33552384 dust /dev/vdb1 0 4096'
+
+::
+
+ $ sudo dmsetup create dust1 --table '0 33552384 dust /dev/vdb1 0 4096'
Check the status of the read behavior ("bypass" indicates that all I/O
-will be passed through to the underlying device):
-$ sudo dmsetup status dust1
-0 33552384 dust 252:17 bypass
+will be passed through to the underlying device)::
+
+ $ sudo dmsetup status dust1
+ 0 33552384 dust 252:17 bypass
-$ sudo dd if=/dev/mapper/dust1 of=/dev/null bs=512 count=128 iflag=direct
-128+0 records in
-128+0 records out
+ $ sudo dd if=/dev/mapper/dust1 of=/dev/null bs=512 count=128 iflag=direct
+ 128+0 records in
+ 128+0 records out
-$ sudo dd if=/dev/zero of=/dev/mapper/dust1 bs=512 count=128 oflag=direct
-128+0 records in
-128+0 records out
+ $ sudo dd if=/dev/zero of=/dev/mapper/dust1 bs=512 count=128 oflag=direct
+ 128+0 records in
+ 128+0 records out
-Adding and removing bad blocks:
--------------------------------
+Adding and removing bad blocks
+------------------------------
At any time (i.e.: whether the device has the "bad block" emulation
enabled or disabled), bad blocks may be added or removed from the
-device via the "addbadblock" and "removebadblock" messages:
+device via the "addbadblock" and "removebadblock" messages::
-$ sudo dmsetup message dust1 0 addbadblock 60
-kernel: device-mapper: dust: badblock added at block 60
+ $ sudo dmsetup message dust1 0 addbadblock 60
+ kernel: device-mapper: dust: badblock added at block 60
-$ sudo dmsetup message dust1 0 addbadblock 67
-kernel: device-mapper: dust: badblock added at block 67
+ $ sudo dmsetup message dust1 0 addbadblock 67
+ kernel: device-mapper: dust: badblock added at block 67
-$ sudo dmsetup message dust1 0 addbadblock 72
-kernel: device-mapper: dust: badblock added at block 72
+ $ sudo dmsetup message dust1 0 addbadblock 72
+ kernel: device-mapper: dust: badblock added at block 72
These bad blocks will be stored in the "bad block list".
-While the device is in "bypass" mode, reads and writes will succeed:
+While the device is in "bypass" mode, reads and writes will succeed::
-$ sudo dmsetup status dust1
-0 33552384 dust 252:17 bypass
+ $ sudo dmsetup status dust1
+ 0 33552384 dust 252:17 bypass
-Enabling block read failures:
------------------------------
+Enabling block read failures
+----------------------------
-To enable the "fail read on bad block" behavior, send the "enable" message:
+To enable the "fail read on bad block" behavior, send the "enable" message::
-$ sudo dmsetup message dust1 0 enable
-kernel: device-mapper: dust: enabling read failures on bad sectors
+ $ sudo dmsetup message dust1 0 enable
+ kernel: device-mapper: dust: enabling read failures on bad sectors
-$ sudo dmsetup status dust1
-0 33552384 dust 252:17 fail_read_on_bad_block
+ $ sudo dmsetup status dust1
+ 0 33552384 dust 252:17 fail_read_on_bad_block
With the device in "fail read on bad block" mode, attempting to read a
-block will encounter an "Input/output error":
+block will encounter an "Input/output error"::
-$ sudo dd if=/dev/mapper/dust1 of=/dev/null bs=512 count=1 skip=67 iflag=direct
-dd: error reading '/dev/mapper/dust1': Input/output error
-0+0 records in
-0+0 records out
-0 bytes copied, 0.00040651 s, 0.0 kB/s
+ $ sudo dd if=/dev/mapper/dust1 of=/dev/null bs=512 count=1 skip=67 iflag=direct
+ dd: error reading '/dev/mapper/dust1': Input/output error
+ 0+0 records in
+ 0+0 records out
+ 0 bytes copied, 0.00040651 s, 0.0 kB/s
...and writing to the bad blocks will remove the blocks from the list,
-therefore emulating the "remap" behavior of hard disk drives:
+therefore emulating the "remap" behavior of hard disk drives::
-$ sudo dd if=/dev/zero of=/dev/mapper/dust1 bs=512 count=128 oflag=direct
-128+0 records in
-128+0 records out
+ $ sudo dd if=/dev/zero of=/dev/mapper/dust1 bs=512 count=128 oflag=direct
+ 128+0 records in
+ 128+0 records out
-kernel: device-mapper: dust: block 60 removed from badblocklist by write
-kernel: device-mapper: dust: block 67 removed from badblocklist by write
-kernel: device-mapper: dust: block 72 removed from badblocklist by write
-kernel: device-mapper: dust: block 87 removed from badblocklist by write
+ kernel: device-mapper: dust: block 60 removed from badblocklist by write
+ kernel: device-mapper: dust: block 67 removed from badblocklist by write
+ kernel: device-mapper: dust: block 72 removed from badblocklist by write
+ kernel: device-mapper: dust: block 87 removed from badblocklist by write
-Bad block add/remove error handling:
-------------------------------------
+Bad block add/remove error handling
+-----------------------------------
Attempting to add a bad block that already exists in the list will
-result in an "Invalid argument" error, as well as a helpful message:
+result in an "Invalid argument" error, as well as a helpful message::
-$ sudo dmsetup message dust1 0 addbadblock 88
-device-mapper: message ioctl on dust1 failed: Invalid argument
-kernel: device-mapper: dust: block 88 already in badblocklist
+ $ sudo dmsetup message dust1 0 addbadblock 88
+ device-mapper: message ioctl on dust1 failed: Invalid argument
+ kernel: device-mapper: dust: block 88 already in badblocklist
Attempting to remove a bad block that doesn't exist in the list will
-result in an "Invalid argument" error, as well as a helpful message:
+result in an "Invalid argument" error, as well as a helpful message::
-$ sudo dmsetup message dust1 0 removebadblock 87
-device-mapper: message ioctl on dust1 failed: Invalid argument
-kernel: device-mapper: dust: block 87 not found in badblocklist
+ $ sudo dmsetup message dust1 0 removebadblock 87
+ device-mapper: message ioctl on dust1 failed: Invalid argument
+ kernel: device-mapper: dust: block 87 not found in badblocklist
-Counting the number of bad blocks in the bad block list:
---------------------------------------------------------
+Counting the number of bad blocks in the bad block list
+-------------------------------------------------------
To count the number of bad blocks configured in the device, run the
-following message command:
+following message command::
-$ sudo dmsetup message dust1 0 countbadblocks
+ $ sudo dmsetup message dust1 0 countbadblocks
A message will print with the number of bad blocks currently
-configured on the device:
+configured on the device::
-kernel: device-mapper: dust: countbadblocks: 895 badblock(s) found
+ kernel: device-mapper: dust: countbadblocks: 895 badblock(s) found
-Querying for specific bad blocks:
----------------------------------
+Querying for specific bad blocks
+--------------------------------
To find out if a specific block is in the bad block list, run the
-following message command:
+following message command::
-$ sudo dmsetup message dust1 0 queryblock 72
+ $ sudo dmsetup message dust1 0 queryblock 72
-The following message will print if the block is in the list:
-device-mapper: dust: queryblock: block 72 found in badblocklist
+The following message will print if the block is in the list::
-The following message will print if the block is in the list:
-device-mapper: dust: queryblock: block 72 not found in badblocklist
+ device-mapper: dust: queryblock: block 72 found in badblocklist
+
+The following message will print if the block is not in the list::
+
+ device-mapper: dust: queryblock: block 72 not found in badblocklist
The "queryblock" message command will work in both the "enabled"
and "disabled" modes, allowing the verification of whether a block
will be treated as "bad" without having to issue I/O to the device,
or having to "enable" the bad block emulation.
-Clearing the bad block list:
-----------------------------
+Clearing the bad block list
+---------------------------
To clear the bad block list (without needing to individually run
a "removebadblock" message command for every block), run the
-following message command:
+following message command::
-$ sudo dmsetup message dust1 0 clearbadblocks
+ $ sudo dmsetup message dust1 0 clearbadblocks
-After clearing the bad block list, the following message will appear:
+After clearing the bad block list, the following message will appear::
-kernel: device-mapper: dust: clearbadblocks: badblocks cleared
+ kernel: device-mapper: dust: clearbadblocks: badblocks cleared
If there were no bad blocks to clear, the following message will
-appear:
+appear::
-kernel: device-mapper: dust: clearbadblocks: no badblocks found
+ kernel: device-mapper: dust: clearbadblocks: no badblocks found
-Message commands list:
-----------------------
+Message commands list
+---------------------
Below is a list of the messages that can be sent to a dust device:
-Operations on blocks (requires a <blknum> argument):
+Operations on blocks (requires a <blknum> argument)::
-addbadblock <blknum>
-queryblock <blknum>
-removebadblock <blknum>
+ addbadblock <blknum>
+ queryblock <blknum>
+ removebadblock <blknum>
...where <blknum> is a block number within range of the device
- (corresponding to the block size of the device.)
+(corresponding to the block size of the device.)
-Single argument message commands:
+Single argument message commands::
-countbadblocks
-clearbadblocks
-disable
-enable
-quiet
+ countbadblocks
+ clearbadblocks
+ disable
+ enable
+ quiet
-Device removal:
----------------
+Device removal
+--------------
-When finished, remove the device via the "dmsetup remove" command:
+When finished, remove the device via the "dmsetup remove" command::
-$ sudo dmsetup remove dust1
+ $ sudo dmsetup remove dust1
-Quiet mode:
------------
+Quiet mode
+----------
On test runs with many bad blocks, it may be desirable to avoid
excessive logging (from bad blocks added, removed, or "remapped").
-This can be done by enabling "quiet mode" via the following message:
+This can be done by enabling "quiet mode" via the following message::
-$ sudo dmsetup message dust1 0 quiet
+ $ sudo dmsetup message dust1 0 quiet
This will suppress log messages from add / remove / removed by write
operations. Log messages from "countbadblocks" or "queryblock"
message commands will still print in quiet mode.
-The status of quiet mode can be seen by running "dmsetup status":
+The status of quiet mode can be seen by running "dmsetup status"::
-$ sudo dmsetup status dust1
-0 33552384 dust 252:17 fail_read_on_bad_block quiet
+ $ sudo dmsetup status dust1
+ 0 33552384 dust 252:17 fail_read_on_bad_block quiet
-To disable quiet mode, send the "quiet" message again:
+To disable quiet mode, send the "quiet" message again::
-$ sudo dmsetup message dust1 0 quiet
+ $ sudo dmsetup message dust1 0 quiet
-$ sudo dmsetup status dust1
-0 33552384 dust 252:17 fail_read_on_bad_block verbose
+ $ sudo dmsetup status dust1
+ 0 33552384 dust 252:17 fail_read_on_bad_block verbose
(The presence of "verbose" indicates normal logging.)
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