DATA_DEV_BLOCK_SIZE_MIN_SECTORS  320 drivers/md/dm-cache-target.c #define DATA_DEV_BLOCK_SIZE_MIN_SECTORS (32 * 1024 >> SECTOR_SHIFT)
DATA_DEV_BLOCK_SIZE_MIN_SECTORS   44 drivers/md/dm-thin.c #define DATA_DEV_BLOCK_SIZE_MIN_SECTORS (64 * 1024 >> SECTOR_SHIFT)