dump compression and variable block sizes

[Chris Cameron]

Gist of the problem is I'm trying to use dump's compression, and it 
gives the error "write error 40 blocks into volume 1: Input/output 
error".

I have no reason to believe the tape drive doesn't support variable 
block sizes (although it does seem to be a crappy drive). I have run 
'mt -f /dev/st0 setblk 0', and tar's -z option works fine (although if 
I understand it correctly, tar and dump compress at different levels). 
The drive is used daily with uncompressed dump.


Can anyone tell if I've done something wrong, or if there's some option 
I haven't set? Any certain way to tell whether this tape drive will do 
variable length blocks?



More information.

>From dmesg:
st: Version 20030406, bufsize 32768, max init. bufs 4, s/g segs 16
Attached scsi tape st0 at scsi0, channel 0, id 6, lun 0

mt status:
SCSI 2 tape drive:
File number=2, block number=0, partition=0.
Tape block size 0 bytes. Density code 0x40 (DLT1 40 GB, or Ultrium).
Soft error count since last status=0
General status bits on (81010000):
 EOF ONLINE IM_REP_EN


Example dump:

[ccameron at cgydc002 ccameron]$ sudo dump -0z -f /dev/nst0 /dev/sda7
Password:
  DUMP: Date of this level 0 dump: Tue Oct 26 11:36:06 2004
  DUMP: Dumping /dev/sda7 (/) to /dev/nst0
  DUMP: Added inode 8 to exclude list (journal inode)
  DUMP: Added inode 7 to exclude list (resize inode)
  DUMP: Label: /
  DUMP: Compressing output at compression level 2 (zlib)
  DUMP: mapping (Pass I) [regular files]
  DUMP: mapping (Pass II) [directories]
  DUMP: estimated 258001 tape blocks.
  DUMP: Volume 1 started with block 1 at: Tue Oct 26 11:36:10 2004
  DUMP: dumping (Pass III) [directories]
  DUMP: write error 40 blocks into volume 1: Input/output error
  DUMP: Do you want to rewrite this volume?: ("yes" or "no") no
  DUMP: Do you want to start the next tape?: ("yes" or "no") no
  DUMP: The ENTIRE dump is aborted.