I've just plugged in my new seagate 4mm DAT drive which probes as:

Jun 22 21:46:30 zen /netbsd: st0 at scsibus1 targ 5 lun 0:\
 <ARCHIVE, Python 02779-XXX, 6280> SCSI2 1/sequential removable

and tried reading a tape written by a borrowed Sun 4mm DAT (also
happens to be an ARCHIVE, Python) which I've been doing my backups on
since my old HP DDS1 drive died.

After one failed attempt, it read the tape, but logged dozens of
errors:

Jun 22 21:54:18 zen /netbsd: st0(aha2:5:0):  Check Condition on opcode 0x8
...
...

dmesg shows:

st0(aha2:5:0):  Check Condition on opcode 0x8
    SENSE KEY:  No Additional Sense
                Incorrect Length Indicator Set
   INFO FIELD:  4096
     ASC/ASCQ:  No Additional Sense Information

st0(aha2:5:0):  Check Condition on opcode 0x8
    SENSE KEY:  No Additional Sense
                Incorrect Length Indicator Set
   INFO FIELD:  6144
     ASC/ASCQ:  No Additional Sense Information

st0(aha2:5:0):  Check Condition on opcode 0x8
    SENSE KEY:  No Additional Sense
                Filemark Detected
   INFO FIELD:  8192
     ASC/ASCQ:  Filemark Detected

Is the drive a dud?  It makes some rather disturbing noises :-)

Yow, I just wrote a tape using:

find lib -print | cpio -oacv | dd bs=8k of=/dev/rst0

(no errors, but it took _ages_ to get ready after putting the tape in)
and then read it using 

dd bs=8k if=/dev/rst0 | cpio -it > /tmp/abc

and root's window went beserk with:

Jun 22 22:14:02 zen /netbsd: st0(aha2:5:0):  Check Condition on opcode 0x8
Jun 22 22:14:02 zen /netbsd:     SENSE KEY:  No Additional Sense
Jun 22 22:14:02 zen /netbsd:                 Incorrect Length Indicator Set
Jun 22 22:14:02 zen /netbsd:    INFO FIELD:  5632
Jun 22 22:14:02 zen /netbsd:      ASC/ASCQ:  No Additional Sense Information

messages.

Trying dd bs=32k just gets me:

Jun 22 22:16:28 zen /netbsd: st0(aha2:5:0):  Check Condition on opcode 0x8
Jun 22 22:16:28 zen /netbsd:     SENSE KEY:  No Additional Sense
Jun 22 22:16:28 zen /netbsd:                 Incorrect Length Indicator Set
Jun 22 22:16:28 zen /netbsd:    INFO FIELD:  30208
Jun 22 22:16:28 zen /netbsd:      ASC/ASCQ:  No Additional Sense Information

instead.  Input appreciated.
(No I can't afford a DLT drive :-)

--sjg