>> If I recall correctly, on exabyte, EOF markers are "1MB" in size (although
>> newer tape formats aren't quite so braindead).  So more files on the tape
>> means less space for real data.  When ypu're backing up in excess of 100,000
>> files onto the one tape, it makes a difference.
>That was true of the original 8200 format. Later formats used on the 8500
>series offered two sizes of tape mark. The long mark, and a short mark
>which chews up some 128k.

Of course, neither tar nor cpio stores one disk file per tape "file".  There
is one EOF mark per tar archive, not per disk file.  If you back up 100,000
files on one tape, you get one EOF mark.  If you do multiple backups per
tape, you have one EOF mark per backup, but you're talking tens, not hundred
thousands, of EOF marks in that case.