Device functionality is encoded in the “Minor number” of device nodes in /dev.

TMSCP Tapes:

This is valid for my TU81+ tape drive.

According to /sys/pdpuba/tm.c, these bits in the minor number modify the tapes behaviour.

Bit 1,0 (mask 0x03): device number 0..3 (by default, only 2 tapes are compiled into the kernel)
Bit 2: (mask 0x04): no rewind flag
Bits 4,3 (mask 0x18): density 0..3: 800, 1600, 6250, not used

For device #0, these are the minor numbers for certain functions:




no rewind

density #0 800bpi



density #1 1600bpi



density #2 6250 bpi




The “rewind” device nodes are “mt”, the “no rewind” nodes are “nmt

I found this in tmscp.c”: Density may only changed at BOT (begin of tape)”

To generate devices nodes for TU81 TMSCP tape drive::

cd /dev
rm mt* rmt* nmt* nrmt*


1. Copy 1 file to tape (test file is the system: “/unix”

# mt rew
# dd if=/unix of=/dev/rmt12 bs=10240

2. Read in with other name “/tstunix”:

# mt rew
# dd if=/dev/rmt12 of=/tstunix bs=10240

3. check, wether restore = original

# diff unix tstunix

Dump and restore:

- use “raw device “rmt*”, not “mt”
- use blocksize bs=10240

* Calc size of dump:

tar cf - | wc -c * 
tar cfv - | dd of=/dev/rmt12 bs=10240

* Check archive content

dd if=/dev/rmt12 bs=10240 | tar tvf -

* Restore files

dd if=/dev/rmt12 bs=10240 | tar xvf - 


TU81+ chache:

Normal: enable TU81+ cache with:

# mt cacheon

Anomalies detected: Verify writing: must cache be flushed????


In tmscp-c steht:

“Enable cache with "sysctl -w machdep.tmscp.cache=0xXXXX".
xxxx =00001 = firstdrive on first ctl
sysctl -w machdep.tmscp.cache=1