Drive inventory

From: jwbirdsa_at_picarefy.com <(jwbirdsa_at_picarefy.com)>
Date: Thu Feb 14 20:20:55 2002

tony writes:
>One nasty that I've come across is that many 9 track QIC24 tape drives
>can do QIC11 as well. And they can do the 4 track QIC11. But you have a
>similar sort of problem to using 40 cylinder disks in 80 cylinder drives.
>Reading is fine, but don't try writing to an already-written tape.

   Actually, it's even a bit funkier than that. I spent a lot of time
messing around with the tape drives that same with Sun-2's (QIC-11) and
Sun-3's (QIC-24). SunOS on a Sun-3 had two devices for each tape drive,
which determined whether it used QIC-11 or QIC-24, and for reading it was
smart enough to autodetect and use the correct format regardless of which
device you used.

   So far so good.

   I started out with Sun-3's, and for a while I didn't think there was
actually any difference between the two devices, since I could get
approximately the same capacity (~60M) on the tape using either one, whereas
QIC-11 is supposed to only be 20M. When I got into Sun-2's, I discovered
that there was a difference, and I had to use the correct device on a -3
when prepping a tape for use on a -2. In addition, I had to be very careful
not to overrun the 20M limit, because the drives in the -2's would only
read 20M, per the spec. As long as I wrote less than 20M, in QIC-11 format,
the tapes would work fine, but I had to enforce the 20M limit manually.

   It took some investigation to discover that the QIC-11 standard was at
some point extended from four tracks to nine tracks, and obviously the
QIC-24 drives used in the -3's supported the extended standard. I wish
SunOS had included a third device to allow distinguishing between
four-track and nine-track QIC-11, but perhaps the drive or the drive/SCSI
bridge didn't provide the necessary pseudo-EOT notification.

   --James B.
Received on Thu Feb 14 2002 - 20:20:55 GMT