Tests 228 and 405 are the only tests that use the make_small_sync() function in sanity-hsm.

Considering the function internally calls:

dd if=/dev/urandom ... conv=sync

That conv=sync means: "pad every input block with NULs to ibs-size; when used with block or unblock, pad with spaces rather than NULs"

And that /dev/urandom does not return short reads, and does not block.

I believe the usefulness of make_small_sync is questionable.