SUMMARY: Tape-Problems

From: Dirk Behrens (
Date: Tue Oct 13 1992 - 15:02:04 CDT

Some weeks ago I ask this questions:

we have some problems with two identically tapedrives, typ Viper 2150S (150 MB).
The two streamers are connected to two different SUN SPARCstation 2 using SUN
OS 4.1.2. We use 150MB cartdriges, typ Sony QD6150. By applieing the "tar"
command we have following problems:

Some tapes are readable and writable from/to TAPE1 and TAPE2. Thats allright!

Some tapes aren't readable or writable from/to TAPE1 but are from/to TAPE2. ???

Some extern written tapes (also SONY QD6150) aren't readable from TAPE1 but are from TAPE2. ???

Extern written tapes from other manufacturer are readable from TAPE1 and TAPE2 !!!

So, TAPE2 seems to have a better work with the SONY-tapes !?!

We send TAPE1 back to the Distibutor, but he tested it exhaustive and found no

Is the Viper Drive a bad one ? Is it very sensitiv about the Media?
Are the SONY Tapes bad ones? Do they need a non-sensity Drive?
Has anybody else such problems with Sony Tapes or Viper Streamer?


I`ve got 4 answers. All said it`s a alignment problem. All said they have no
problems with Sony - tapes. It`s a well known problem with 150 MB Streamer. With DAT perhaps this would be no problem. The distributor tested only reading and writing with this one Tape. By sending the tape back and replacing the tapedrive all works fine.

Thanks for replies by
Mike Raffety <>

Two answers are following: wrotes:

 It sounds like an alignment problem. Any mechanical device has tolerances.
It sounds like both your drives are within the accepted tolerance range but
are off of the nominal setting ( the middle of the road) in opposite
directions. This accentuates the variance. Everyone elses drives also vary
fromnominal to some degree. If they vary in the same direction as your drive
there is no problem. If they vary in the other direction, and vary enough, than
there is a problem. Unfortunately you cannot adjust the alignment of a QIC
drive in the field. ( This maybe a blessing because it means that once set
properly in the depot they hold their alignment better) My beleif is that we
are seeing more problems with the QIC-150 drives than we did with QIC-24 drives
because the track width is much narrower leaving less 'slop' on either side of
nominal. I would suggest replacing the drive that has trouble reading tapes
from the widest variety of sources.

-- Bob Smart Net -

------------------------------------------- wrotes:

It sounds to me like TAPE1 may have a problem with its head alignment.

For discussion, suppose that "perfect" alignment is 0Q and the maximum
permissible deviations are +0.5Q and -0.5Q. (I am being deliberately
vague about just what Q stands for, or what its units are, since I am
not familiar in detail with what the relevant factors are. Also, this
is an oversimplification since the there are also specifications and
tolerances which apply to the media.)

The drives are designed such that they can handle a deviation of 1.0Q
between reader and writer, but any more than that is likely to cause
problems. It is reasonable to expect that the severity and
reproduceability of the problems will be related to the size of the

Now if TAPE1 is at +0.55Q and TAPE2 is at -0.48Q then the deviation
between them will be 1.03Q and their interoperability will be flakey.
TAPE1 will interoperate properly with any drive whose Q >= -0.45 but
will fail with drives where -0.5 <= Q < -0.45 even though those drives
are within specification. This could explain why it fails on some (but
apparently not all) externally written QD6150 tapes.

If the tape used is sufficiently better than spec, that may somehow
make up for excess deviation and allow interoperation. This could
explain why externally written tapes from another manufacturer seem to
work properly. It is also possible that there is NO functional
difference in the tapes, rather the other manufacturer's tapes just
happen to have been written on a drive whose Q > -0.45

> We send TAPE1 back to the Distibutor, but he tested it exhaustive and
> found no failure.

Did he check

* head alignment

* interoperability with other drives

* using Sony QD6150 tapes

or did he just verify that it could read back what it wrote?

> Are the SONY Tapes bad ones?

I have not had problems with Sony tapes.


Dipl.-Ing. Dirk Behrens University of Hannover
                                        Institute for Microelectronic Systems
                                        Callinstrasse 34
Phone : +49 511 762-4986 W-3000 Hannover 1
Telefax: +49 511 762-4994 Germany


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