SUMMARY:2.3GB/5GB exabyte compatibility

From: John Moran JL/OD (
Date: Wed Oct 07 1992 - 12:54:29 CDT

Hi all,

my original question:

>I am in the process of buying a number of 5GB exabyte units to use
>in conjunction with my original 2.3GB units. There has been a lot
>of information on this recently on the net of which the claim that
>one can't use a tape previously dumped on a 2.3GB unit worries me.
>I gather from the tape distributors that there is no physical
>difference between the tapes so I guess that it has to do with the
>tape label. Or what..? Isn't it possible to use "mt -erase" to
>erase the label? I would appreciate any info from anyone using
>mixed units and will of course summarize to the net

I received 23 replies of which (Glenn Satchell) from ups!upstage!glenn@fourx.Aus.Sun.COM formulated it best:

If you are running 4.1.1 the st driver cannot send the density change
ioctl's so the drive auto senses. Unused tapes will work at 5GB. If the
tape already has data on it the drive senses this and uses 2.3GB mode.
If you use 'mt erase' on a used tape it will work fine in 5GB mode,
although it takes about 2.5 hours to erase.

In the doco that comes with the Sun 5GB unit it states that under sunos
4.1.2 or later the device will write in 2.3GB mode if:

a) you use the /dev/rst0 device
b) you use a tape previously written in 2.3GB mode and you are not at
   the beginning of tape marker

It will write in 5GB mode if:

a) you use the /dev/rst8 device
b) the tape is new or you are at the beginning of tape

I have not personally tested this but it is the overall consensus.

Many thanks to all who took the time to answer my question.

best regards

John Moran

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