scsi tape: does kernel give wrong info to cpio?

[Giulio Orsero]

I'm posting here because redhat/bugzilla moved my bug report
from cpio to kernel, so they think this is a kernel/scsi issue.

==

kernel 2.2.14, cpio-2.4.2-13 (rh61)
scsi_mod, aha152x, st as modules
SCSI controller: Adaptec AVA-1050
SCSI tape unit: Tandberg SLR2 525MB

PROBLEM:
I can do multivolume cpio backups on tape, but then
I cannot restore them due to cpio problems, maybe due to the kernel.

I use these commands:

Backup:
find /path|cpio -ovHcrc -O /dev/st0  
- it starts to backup then it asks me for a 2nd tape with:
"Found end of tape.  Load next tape and press RETURN."
I insert the 2nd tape and the backups ends regularly with
the message about the blocks copied.


Restore:
cpio -ivdumHcrc -I /dev/st0 
- it asks me for the 2nd tape with:
"Found end of tape.  Load next tape and press RETURN."
- then asks me for a 3rd tape!!, with:
"Found end of tape.  Load next tape and press RETURN."
Since I have not a 3rd tape (the backup took 2 tapes only),
I simply press enter (_leaving_ the 2nd tape IN)
"cpio: read error: No medium found" (the 2nd tape is in).

Note that:
- The stuf restored is only 5/10k smaller than the original 
size,very little but the restore is unreliable.
- the backup took very little of the 2nd tape (say 10MB).
- I even tried with -B 5120
- I tried with different tapes (3M), different controllers 
(all ISA adaptec with module aha152x.o) and different tape
units (all Tandberg)

I found an article on dejanews by Kai Mäkisara regarding problems 
with cpio  multivolume restore with kernels 2.0.x (cpio quits
as soon as it arrives at the end of the 1st tape with an
I/O error).
I found nothing regarding kernels 2.2.x.

===begin deja article on 2.0.x kernels 
On Tue, Mar 24, 1998 at 11:26:10AM +0100, Stephane KLEIN 
wrote:
> But the restoring (cpio -i ..) fails at the end of the 
first tape with a
> read IO error.

I think this is a known bug in 2.0.X. The following message 
is from Kai
Mäkisara, maintainer of the SCSI tape driver:

| On Wed, 28 May 1997, Jan Echternach wrote:
| > There is a problem with taper not detecting the end of 
tape. With my
| > SCSI DAT drive and kernel 2.0.30, read() returns 0 only 
one time, and
| > all subsequent reads return EIO. It seems that ftape 
returns _two_
| > times 0, which taper handles correctly.
| > 
| ...
| > 
| > Do 2.1.x kernels return two times 0? If so, should 
2.0.30 also return
| > two times 0 at end of tape?
| > 
| What should happen, according to the BSD semantics, is 
this:
| - at filemark, the first read returns 0 bytes, the second 
read returns
|   data from the next file
| - at EOD, the first and the second read return 0 bytes, 
the third returns
|   error (-1)
| i.e., 2.1.x operates correctly.
| 
| The EOD behaviour was fixed at 2.1.20. In principle, it 
should be fixed
| also at 2.0.31 but I think the risks are too big: fixing 
EOD behaviour
| may break something else (the fix from 2.1.20 can't be 
used directly).
| 
|         Kai

===end deja article

Thanks.

-- 
giulioo en pobox.com

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