How can I recover files off this disk that won't mount?
Disk4 is the whole disk device and no slice with an (HFS) file system. The output is the content of block0 omitting most lines containing only zeros. Block zero often is equivalent to the MBR/pMBR of a disk. Block0 doesn't contain a file system!



To verify/repair a file system, you have to choose a particular partition and the volume has to be mounted. The common external disk has two partitions: the EFI and the main volume - so try:

sudo fsck_hfs -f /dev/disk4s2


If the external disk has more than one visible volume, enter diskutil list and choose the appropriate partition (e.g disk4s3 or disk4s4).



If fsck_hfs fails to mount and/or repair the disk, try a data recovery tool like Data Rescue, R-Studio, Disk Drill etc.

If they also fail contact a professional data recovery specialist like Kroll Ontrack.