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dm-flakey

The dm-flakey target is similar to the dm-linear target, except that it periodically exhibits unreliable behavior. This target is useful for simulating failing devices during testing. In the case of zoned block devices, simulating write errors to sequential zones can help to debug application write-pointer management.

dm-flakey works like this: at the time the table is loaded, the device does not generate errors for some seconds (up time), but then exhibits unreliable behavior for down seconds. This cycle then repeats.

Error modes​

Several error-simulation behaviors can be configured.

  • drop_writes All write I/Os are silently ignored and dropped. Read I/Os are handled correctly.
  • error_writes All write I/Os are failed with an error signaled. Read I/Os are handled correctly.
  • corrupt_bio_byte During the down time, replace the Nth byte of the data of each read or write block I/O with a specified value.

The default error mode is to fail all I/O requests during the down time of the simulation cycle.

Zoned Block Device Restrictions​

The same zone alignment restrictions that apply to the dm-linear target also apply to dm-flakey.

Examples​

dm-flakey detailed documentation and usage examples can be found in the kernel source code documentation file Documentation/admin-guide/device-mapper/dm-flakey.rst.