>Depends on whether the combined length of the three files on the tape is
 >shorter, longer, or the same as those overwritten.

	mt -f /dev/nrst0 fsf 3		(skip over the first three >files)

 >If new length == old length, you're now at the beginning of file four,
 >and you can recover it and five with 'tar'.

 >If new length < old length, "mt -f /dev/nrst0 fsf 1" again should put
 >you at the beginning of file four.

 >If new length > old length, the tape is now positioned somewhere inside
 >of the old file four.  That one is probably not recoverable, but
 >"mt -f /dev/nrst0 fsf 1" should put you at the beginning of file five.

When I use mt -f /dev/nrst0 fsf 3

The mt command cannot go over the current EOF of the 3 files backuped. 
ie it won't go beyond to the previous files which have not been overwritten.

After the mt -f /dev/nrst0 fsf 3 command

I use the star -b64 -vt -f /dev/nrst0

It responsed with

bash-2.05b# star -b64 -vt -f /dev/nrst0 

star: Hard EOF on input, first EOF block is missing.

Any suggestion?

David Kwok