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Diffstat (limited to 'Documentation/admin-guide/device-mapper/dm-dust.txt')
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diff --git a/Documentation/admin-guide/device-mapper/dm-dust.txt b/Documentation/admin-guide/device-mapper/dm-dust.txt deleted file mode 100644 index 954d402a1f6a..000000000000 --- a/Documentation/admin-guide/device-mapper/dm-dust.txt +++ /dev/null @@ -1,272 +0,0 @@ -dm-dust -======= - -This target emulates the behavior of bad sectors at arbitrary -locations, and the ability to enable the emulation of the failures -at an arbitrary time. - -This target behaves similarly to a linear target. At a given time, -the user can send a message to the target to start failing read -requests on specific blocks (to emulate the behavior of a hard disk -drive with bad sectors). - -When the failure behavior is enabled (i.e.: when the output of -"dmsetup status" displays "fail_read_on_bad_block"), reads of blocks -in the "bad block list" will fail with EIO ("Input/output error"). - -Writes of blocks in the "bad block list will result in the following: - -1. Remove the block from the "bad block list". -2. Successfully complete the write. - -This emulates the "remapped sector" behavior of a drive with bad -sectors. - -Normally, a drive that is encountering bad sectors will most likely -encounter more bad sectors, at an unknown time or location. -With dm-dust, the user can use the "addbadblock" and "removebadblock" -messages to add arbitrary bad blocks at new locations, and the -"enable" and "disable" messages to modulate the state of whether the -configured "bad blocks" will be treated as bad, or bypassed. -This allows the pre-writing of test data and metadata prior to -simulating a "failure" event where bad sectors start to appear. - -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 - (minimum 512, maximum 1073741824, must be a power of 2) - -Usage instructions: -------------------- - -First, find the size (in 512-byte sectors) of the device to be used: - -$ 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' - -(For a device with a block size of 4096 bytes) -$ 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 - -$ 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 - -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: - -$ 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 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: - -$ sudo dmsetup status dust1 -0 33552384 dust 252:17 bypass - -Enabling block read failures: ------------------------------ - -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 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": - -$ 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: - -$ 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 - -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: - -$ 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: - -$ 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: --------------------------------------------------------- - -To count the number of bad blocks configured in the device, run the -following message command: - -$ sudo dmsetup message dust1 0 countbadblocks - -A message will print with the number of bad blocks currently -configured on the device: - -kernel: device-mapper: dust: countbadblocks: 895 badblock(s) found - -Querying for specific bad blocks: ---------------------------------- - -To find out if a specific block is in the bad block list, run the -following message command: - -$ 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: -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: ----------------------------- - -To clear the bad block list (without needing to individually run -a "removebadblock" message command for every block), run the -following message command: - -$ sudo dmsetup message dust1 0 clearbadblocks - -After clearing the bad block list, the following message will appear: - -kernel: device-mapper: dust: clearbadblocks: badblocks cleared - -If there were no bad blocks to clear, the following message will -appear: - -kernel: device-mapper: dust: clearbadblocks: no badblocks found - -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): - -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.) - -Single argument message commands: - -countbadblocks -clearbadblocks -disable -enable -quiet - -Device removal: ---------------- - -When finished, remove the device via the "dmsetup remove" command: - -$ sudo dmsetup remove dust1 - -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: - -$ 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": - -$ sudo dmsetup status dust1 -0 33552384 dust 252:17 fail_read_on_bad_block quiet - -To disable quiet mode, send the "quiet" message again: - -$ sudo dmsetup message dust1 0 quiet - -$ sudo dmsetup status dust1 -0 33552384 dust 252:17 fail_read_on_bad_block verbose - -(The presence of "verbose" indicates normal logging.) - -"Why not...?" -------------- - -scsi_debug has a "medium error" mode that can fail reads on one -specified sector (sector 0x1234, hardcoded in the source code), but -it uses RAM for the persistent storage, which drastically decreases -the potential device size. - -dm-flakey fails all I/O from all block locations at a specified time -frequency, and not a given point in time. - -When a bad sector occurs on a hard disk drive, reads to that sector -are failed by the device, usually resulting in an error code of EIO -("I/O error") or ENODATA ("No data available"). However, a write to -the sector may succeed, and result in the sector becoming readable -after the device controller no longer experiences errors reading the -sector (or after a reallocation of the sector). However, there may -be bad sectors that occur on the device in the future, in a different, -unpredictable location. - -This target seeks to provide a device that can exhibit the behavior -of a bad sector at a known sector location, at a known time, based -on a large storage device (at least tens of gigabytes, not occupying -system memory). |