Steps to reproduce: A (large) TAR archive has been written to a raw disk /dev/da4. The disk (1TB) is much larger than the archive (160GB). Restoring a single file may take a long time, as tar reads all the way to the end of the archive. This can be solved with the -q option: $ tar -xzOqf /dev/da4 myfile | md5sum Result is the same, only much faster. The checksum is correct. So far so good, but when tar is in a pipeline, it is slow again: $ dd if=/dev/da4 bs=64k | tar -xzOqf - myfile | md5sum Actual result: It appears the -q option does not work when archive is stdin (-f-) This looks like a bug of the (bsd)tar program. Expected result: I expected that the tar program would exit and close its input and output after retrieval of 'myfile'. This would break the pipe to dd, and it would stop as well. Anyway, if dd is killed manually after the md5sum cpu usage has fallen to 0%, the correct result is shown. It would be nice if killing is not needed.
I would recommend submitting an issue in libarchive's tracker, at https://github.com/libarchive/libarchive