dump is reporting 64kB of block size regardless of -b argument. # dump -a -h0 -b32 -C16 -f /mnt/disk2/disk1.dump /dev/gpt/disk1 DUMP: Date of this level 0 dump: Mon Mar 8 23:48:13 2021 DUMP: Date of last level 0 dump: the epoch DUMP: Dumping /dev/gpt/disk1 to /mnt/disk2/disk1.dump DUMP: mapping (Pass I) [regular files] DUMP: Cache 16 MB, blocksize = 65536 DUMP: mapping (Pass II) [directories] DUMP: estimated 2665 tape blocks. DUMP: dumping (Pass III) [directories] DUMP: dumping (Pass IV) [regular files] DUMP: DUMP: 2520 tape blocks on 1 volume DUMP: finished in less than a second DUMP: Closing /mnt/disk2/disk1.dump DUMP: DUMP IS DONE