Need Help With SCSI Tape Drive Interface

Need Help With SCSI Tape Drive Interface

Post by smi.. » Fri, 08 Nov 1991 02:26:26

We have a DECStation 5000/200 running Ultrix 4.2 and are doing IO to Exabyte
tape drives.  The manual for the drives gives information on the SCSI commands
it will accept.  How can I issue one of these command either from within a C
program or from the unix xommand line?
I have been able to obtain rudimentary control using the ioctl function within
C and the mt command from the OS but these don't offer all the commands the
drives claim to acknowledge.
Please send e-mail as I posted this message to several groups none of which I
read frequently.

Thanx in advance
I knew how the game was going to end when I took Brenda
        into the filing room but I took her in anyway.  --Al
They have one big advantage over us:
                *they* know where they're going.        --Batman
Has your family tried 'em, Powdermilk?                  --Garrison Keillor

/* Jeffery G. Smith, BS-RHIT (AKA Doc. Insomnia, WMHD-FM)       *
 *    The Ohio State University, Graduate Physics Program       *
 *        3193 Smith Lab, Columbus, OH 43210  (614) 292-5321    *


1. Help needed with Tandberg TDC3800 SCSI tape drive

I have been trying to 'dump' a backup of my FreeBSD 2.2.5-RELEASE system
onto a Tandberg TDC-3800 SCSI tape amd I am confused.

The tape drive supports QIC-525 and QIC-150 formats which I believe are
26 tracks at 16000 BPI and 18 tracks at 10000 BPI respectively.  I can
used 'mt' to set density to either of the above, and as I want to dump
to DC6150 tapes (150Mb, 620 feet) I set the density to QIC-150.

Using 'mt status' gives the following:

Present Mode:   Density = QIC-150      Blocksize = 512 bytes
---------available modes---------
Mode 0:         Density = 0x00         Blocksize variable
Mode 1:         Density = X3.136-1986  Blocksize = 512 bytes
Mode 2:         Density = X3.39-1986   Blocksize variable
Mode 3:         Density = X3.54-1986   Blocksize variable

Which I don't fully understan as none of the mentioned densities are

I also believe that the QIC drives are not too good at finding the
end-of-tape marker, requiring that a specific amount of data is written

'df -k' shows that the usr filesystem has 859842 1K blocks used.
Assuming a DC6150 tape can hold 150Mb, then I need about 6 tapes to back
it up.  

To dump the /usr filesystem to tape, I used the following command:

dump -0 -d 10000 /usr

which reports that it needs 4.2 tapees, which doesn't sound right.  I
let it continue and it failed after 155456 blocks, which does sound
about right assuming 1K tape blocks.

Next I tried using the -s option to dump to specify the tape length, I
tried 620 feet, as that it what it says on the tape housing.  Now it
tells me it needs over 10 tapes.

As it didn't seem to be working, I tried the -B option to specify the
number of blocks per tape.  I set this to 155450, and it told me it
needed 6.13 tapes, which sounds OK.  Now the problem is, if i use a
DC6525 tape (525Mb) and use -B '525Mb worth of blocks', how does the
tape drive know to write at 16000 BPI rather than 10000 BPI?

I seem to be missing something important here.  Can anyone point me in
the right direction to understand this?


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