On Wed, 2 Jun 1999, Russell Berry wrote:
> First, my humblest apologies for asking this 'barely-scsi' related item on the
> list, I'm really desperate for input on this. Scenario:
>
> 1) I do backups to a seagate 2/4G DAT using dump
> 2) I set the tape block size to 16384 using mt -f /dev/st0 setblk 16384
> 3) Three dump files are created, for /, /usr, and /home, respectively
> 4) Made huge system changes, like re-installing everything (system ran
> everything from kernel 1.1.something to current 2.2.9.
> 5) Experienced 'brain-fart' and decided to dump /usr/src to tgz file on tape.
> 6) Stopped tape after overwriting my ONLY good backup 6M using 1024 block size
>
> so there's the dilemma, I could care less about the first dump file /, and I
> know it spanned 71785 blocks, (now these blocks counted as dump blocks of 1024
> bytes, not tape blocks of 16384) To read the tape at all I have to setblk
> 1024, and I thought I could then set a file mark, mt -f /dev/nst0 setblk 16384,
> and seek to the next file marker and I'd be set. But nooooooooooooo. I get
> incorrect block size IO errors if I try to read at this point at either block
> size.
>
> I see two possible solutions, but have been unsuccessful in attaining the
> proper results in my attempts. The first solution would be to find a way to
> force read the entire tape into a file using dd, and then parsing that file
> through whatever means deemed necessary. The Second is what I've been trying,
> to calculate the exact position, and squash the IO errors as to force read at
> that point using restore.
>
> Any solutions, suggestions, guesses, hammers more than welcome! I really need
> this data, there's 3 years of work on there!
Tough luck. The SCSI drives have very complex operatings systems and on
board controllers. Basically, the firmware will strictly refuse to read
anything beyond the overwritten part. A faulty firmware might have skipped
with setblk but yours obviously didn't. There might be vendor specific
commands beyond the SCSI command set to read back these blocks, but who
would know them? I also heard about a specific tape drive where a serial
line could be connected and a special diagnose mode entered and data read
beyond end of data.
Alas, I might be wrong and I don't know the name of it anymore too. Maybe
one of these data recovery companies with specific hardware can help you,
otherwise you're toasted.
This, btw, is the reason why one never should append to an existing tape
backup. The risk to destroy it is too high.
Michael.
--
Michael Weller: [EMAIL PROTECTED], [EMAIL PROTECTED],
or even [EMAIL PROTECTED] If you encounter an eowmob account on
any machine in the net, it's very likely it's me.
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