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This is an experiment in TRIM support for MD devices. It basically creates a large file (using the fallocate() syscall), then uses hdparm tool to get information about file extents, maps them to physical device addresses and calls TRIM on them. To make sure that we're really trimming the right data, mdtrim writes random data at the beginning, end and some middle parts of the extent and makes sure that this data is read correctly using direct IO on the block device. Should be fairly safe if I haven't messed up with logical-to-physical sector translation too much. The test/test.sh script can be used to test it. WARNING! While mdtrim.py is fairly safe, test.sh script is definitely NOT safe as it formats the drive which is used to do testing.