[Bug-tar] compression and autodetection issues when working with tape drives

[Michael Postmann]

Hello!

I have a SCSI-2 DDS2 Tape drive and got several issues when trying to 
use compression (gzip, bzip2) on backups.

Here you can see a sample session:

address@hidden test2]# ls -lah
total 20K
drwxr-xr-x    2 root     root         4.0K Sep  7 12:00 .
drwxr-xr-x    4 root     root         4.0K Sep  7 11:08 ..
-rw-r--r--    1 root     root           41 Sep  7 12:00 IDENTITY
-rw-r--r--    1 root     root           12 Sep  7 11:07 NAME
-rw-r--r--    1 root     root           30 Sep  7 11:07 TIMESTAMP
address@hidden test2]# cat *
2bc53e31a3ae13a7ac4256d9132dfd2215398dc6
Testtape #1
Wed Sep  7 11:07:31 CEST 2005
address@hidden test2]# mt rewind
address@hidden test2]# mt status
SCSI 2 tape drive:
File number=0, block number=0, partition=0.
Tape block size 0 bytes. Density code 0x24 (DDS-2).
Soft error count since last status=0
General status bits on (41010000):
BOT ONLINE IM_REP_EN
address@hidden test2]# mt tell
At block 0.
address@hidden test2]# tar cvf /dev/nst0 *
IDENTITY
NAME
TIMESTAMP
address@hidden test2]# mt rewind
address@hidden test2]# tar xvf /dev/nst0
IDENTITY
NAME
TIMESTAMP
address@hidden test2]# mt rewind
address@hidden test2]# tar czvf /dev/nst0 *
IDENTITY
NAME
TIMESTAMP
address@hidden test2]# mt rewind
address@hidden test2]# tar xzfv /dev/nst0
IDENTITY
NAME
TIMESTAMP
address@hidden test2]# mt rewind
address@hidden test2]# tar xvf /dev/nst0

gzip: stdin: unexpected end of file
tar: Child returned status 1
tar: Error exit delayed from previous errors
address@hidden test2]# mt rewind
address@hidden test2]# tar cjvf /dev/nst0 *
IDENTITY
NAME
TIMESTAMP
address@hidden test2]# mt rewind
address@hidden test2]# tar xjvf /dev/nst0

bzip2: (stdin): trailing garbage after EOF ignored
IDENTITY
NAME
TIMESTAMP
address@hidden test2]# mt rewind
address@hidden test2]# tar xvf /dev/nst0

bzip2: Compressed file ends unexpectedly;
       perhaps it is corrupted?  *Possible* reason follows.
bzip2: Invalid argument
       Input file = (stdin), output file = (stdout)

It is possible that the compressed file(s) have become corrupted.
You can use the -tvv option to test integrity of such files.

You can use the `bzip2recover' program to attempt to recover
data from undamaged sections of corrupted files.

tar: Child returned status 2
tar: Error exit delayed from previous errors
address@hidden test2]# tar --version
tar (GNU tar) 1.15.1


When I do not use compression all works fine so I think it's not a 
kernel/driver/device issue.

I hope this helps you to help me and lots of other people.

thx in advance

Michael Postmann