SUMMARY: How do I retension an 8mm tape?

From: Marc Gibian (
Date: Tue Jun 13 1995 - 07:58:15 CDT

My original question:

>> I am doing backups using a Sun 8mm tape drive and tapes that have been
>> sitting unopened in a box for well over a year. Recently, I started
>> having backup failures due to tape errors. I manually retried one
>> particular tape and it would work up to and past the point of each
>> error until it finally worked, which sure sounds like I really just
>> need to retension my tapes before I try to use them. Unfortunately, my
>> SunOS 4.1.3 mt command does not permit a retension on the 8mm drive
>> and all other commands I can think of stop at the end of existing data
>> (unless it is trying to write data, in which case I'm back doing
>> manual retries until things work).
>> Anyone know how to convince SunOS to retension the tape on an 8mm drive?

I recieved a number of reasonable solutions as well as a few
mis-conceptions about 8mm drives.

1. Use the "mt fsf x" command with x set to 100/101/1000 depending on
what works for you, issuing it multiple times, ignoring logical EOT
error messages.

2. Buy a bi-directional 8mm rewinder (intended for 8mm video usage) or
use an 8mm camcorder.

3. Use "mt erase". It takes several hours but it always goes to the
end of the tape and back.

4. Do a "mt eom" followed by a "mt rewind". I found that this does not
go to the real end of the tape in my experience.

5. Use PDC's BudTool.

6. Do a "cat /dev/zero > /dev/rst#".

7. Make sure you clean the heads in the drive regularly.

8. Just "mt retension". WRONG... that operation is not supported by
8mm drives.

9. You don't need to retension 8mm tapes due to their
technology. WRONG... if you leave a tape unused long enough, it tends
to stick together and thus needs to be retensioned.

My thanks to:

John Rosenberg <> (S. D. Raffensberger 500622500 (RD)) (Stan Hoffman)
FV Admin mail <> (Tom Schmidt) (Rick Dempster) (Frode Stromsvag) (Sean Ward)
EDM@MOG.WR.USGS.GOV (Ed Maple, U.S. Geological Survey)
Phillip Millman <> (Donald McLachlan) (Kohler R. P. (Robert)) (Kevin West)
Ray Brownrigg <> (David McCall) (Peter (jaffa cake) Allan) (John Hearns - System Manager)
mshon@sunrock.East.Sun.COM (Michael J. Shon {*Prof Services} Sun Rochester) (James Wetterau)

Marc S. Gibian
Telos Consulting Services phone: (617) 377-6350
PRISM/TFS email:

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