Subject: Re: Putting tapes in varblock mode
To: John F. Woods <>
From: David Gilbert <>
List: current-users
Date: 03/29/1996 20:28:52
>>>>> ""John" == "John F Woods" <> writes:

John> This is IBM you're talking about.  They probably figure that
John> half-inch 800BPI reel-to-reel tape drives still dominate the
John> earth.

John> I'm pretty sure none of the QIC standards permit anything other
John> than 512 bytes per block.

	I have done most of the tape support that our company
supports, and can comment on this issue.

	In general, 1/2", 8mm, and 4mm tapes support variable blocks
with varying degrees of the word 'variable'.  In general 1/4" do not.
I have an example of a QIC format that uses variable blocks, and a
drive that works this way... but this confuses the heck out of most
1/4" drives (and indeed was hard to support, but we were forced to).

	1/2" tape drives will almost always do the full list (save
EOM) of operations that UN*X drivers provide.  4mm is generally next
in line supporting most if not all operations (including EOM).  8mm
and QIC fall last, IMHO.  They often do not support appending (which
is a hardware issue, sometimes, for QIC).  QIC does tend to have
better movement support than 8mm.  I have an 8mm that will FSR and
FSF, but not BSR or BSF (only REW).

	In general, I would choose 4mm as the modern tape of choice.
tar -u and tar -r both work with 4mm's that I've tried.  They also fit
in your pocket better.


|David Gilbert, PCI, Richmond Hill, Ontario.  | Two things can only be     |
|Mail:         |  equal if and only if they |
|               |   are precisely opposite.  |