SCSI tape problems

[T. Horsnell]

>T. Horsnell wrote:
>...
>> The problem appears to be that the tapes drop records
>> when being written, but that this can be fixed by increasing
>> the blocksize.
>...
>
>Are you sure that it is during the write operation?
>
>> [root at ls1 ~]$ dd if=tapetest500K of=/dev/st1 bs=10240 ; dd if=/dev/st1 of=junk bs=10240 ; cmp tapetest500K junk
>> 48+1 records in
>> 48+1 records out
>> 36+1 records in
>> 36+1 records out
>> tapetest500K junk differ: byte 215041, line 854
>
>If you add another
>
>dd if=/dev/st1 of=junk2 bs=10240
>
>does that equal junk or is the error in another position?

[root at ls1 ~]$ dd if=tapetest500K of=/dev/st1 bs=10240 ; dd if=/dev/st1 of=junk bs=10240 ; cmp tapetest500K junk
48+1 records in
48+1 records out
34+0 records in
34+0 records out
tapetest500K junk differ: byte 153601, line 593
[root at ls1 ~]$ dd if=/dev/st1 of=junk2 bs=10240; cmp junk junk2
34+0 records in
34+0 records out
[root at ls1 ~]$ dd if=tapetest50M of=/dev/st1 bs=10240 ; dd if=/dev/st1 of=junk bs=10240 ; cmp tapetest50M junk
4882+1 records in
4882+1 records out
2576+1 records in
2576+1 records out
tapetest50M junk differ: byte 153601, line 628
[root at ls1 ~]$ df -k .
Filesystem           1K-blocks      Used Available Use% Mounted on
/dev/sda7              1004024    456760    496260  48% /
[root at ls1 ~]$ dd if=/dev/st1 of=junk2 bs=10240
2576+1 records in
2576+1 records out
[root at ls1 ~]$ diff junk junk2

Furthermore, looking at the byte position at which cmp fails,
its always on an exact record boundary. Also, I have a tape utility
which can tell me the size of tape records. Using this I
see that the last record (the fractional part if the filesize
is not an integral number of tape-blocks) is always the correct size
(I dont know whether it has the correct contents).

The problem still occurs if I make the filesize an integral number
of tape-records.

I'll put the tapelibrary back on my Alpha box and check what
I get when I read tapes which were written on the Opteron.
This should clinch the theory that its a write problem
(or not, as the case may be)

>
>The library has two drives, right? Is it a problem on
>both drives?

Yes. (See the end of my first post).

Cheers,
Terry.

>
>Mogens
>
>-- 
>Mogens Kjaer, Carlsberg A/S, Computer Department
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