SCSI Travan tape drive is flaky

[Trevor Blackwell]

I have a 10/20 GB Seagate Travan tape drive:

FreeBSD 4.7-RELEASE #1: Fri Jan 24 08:05:09 GMT 2003
...
ahd1: <Adaptec 7901A Ultra320 SCSI adapter> port
0x5c00-0x5cff,0x6000-0x60ff mem 0xd0402000-0xd0403fff irq 22 at 
device 3.1 on pci4
aic7901A: Ultra320 Wide Channel B, SCSI Id=7, PCI 33 or 66Mhz, 512 SCBs
...
sa0 at ahd1 bus 0 target 4 lun 0
sa0: <Seagate STT20000N 6A51> Removable Sequential Access SCSI-2 device 
sa0: 10.000MB/s transfers (10.000MHz, offset 15)

When I write to it, it gives up (writes less than a block) randomly
after using only a fraction of the tape, anywhere from 1 to 2 GB. I've
never gotten more than 2 GB written to it. I've tried with 2 different
10/20 GB tapes. For instance:

# mt erase; mt rewind; dd if=tlb-usr.dump0.gz of=/dev/nsa0 bs=65536
dd: /dev/nsa0: short write on tape device
13191+0 records in
13190+1 records out
864442368 bytes transferred in 944.588678 secs (915152 bytes/sec)

[It moved 864 MB of 7706 MB in the file]

Afterwards, mt errstat says:

# mt errstat
Last I/O Residual: 0
 Last I/O Command: 0A 00 01 00 00 00 00 00 00 00 00 00 00 00 00 00
   Last I/O Sense:

         F0 00 03 00 0A F8 00 0A 00 00 00 00 0C 00 00 00
         00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00

Last Control Residual: 0
 Last Control Command: 1A 00 0F 00 1C 00 00 00 00 00 00 00 00 00 00 00
   Last Control Sense:

         70 00 05 00 00 00 00 0A 00 00 00 00 24 00 00 C0
         00 02 00 00 00 00 00 00 00 00 00 00 00 00 00 00

(I can't find a reference for interpreting this) and further writes
fail:

# dd if=tlb-usr.dump0.gz of=/dev/nsa0 bs=65536
dd: /dev/nsa0: Operation not permitted
1+0 records in
0+0 records out
0 bytes transferred in 0.033122 secs (0 bytes/sec)
# whoami
root

It is able to read back the written data:

# mt rewind; tcopy
file 0: block size 65536: records 0 to 13190
file 0: block size 22528: record 13190
file 0: eof after 13191 records: 864442368 bytes

Any suggestions?

-- 
Trevor Blackwell      tlb at tlb.org          (650) 776-7870