On Mon, Dec 07, 2009 at 03:54:32PM -0500, George Sinclair wrote:
> 1. Aside from a data recovery service, is there any way to recover
> data from a NW volume after you re-label it?

Given the media you're likely to be using in 2009, nope.

> Clearly, the previous data is there. It's not like NW overwrites and
> erases all the data on the tape when you label it. It just puts a
> new volume label on it at the beginning, right? OK, so any way to
> run Unix 'dd' or maybe scanner or something wherein you could
> somehow pipe it to 'uasm -r'?

No, because it's the device (the drive and the tape media) that aren't
giving it up, not Networker hiding it.

After writing to media, the drive puts a marker on the media and will
refuse to read past the marker.  So you can "never" read past the last
write marker.  Presumably a recovery house has drives with alternate
firmware that aren't encumbered by the same restrictions.

I've even trie powering down a drive in mid-write so that it would be
unable to record the marker.  This was on a DLT.  The one time I tried
it, I couldn't read past it (got lots of sync errors).  This method has
been mentioned in the past, but I don't know if my attempt failed
because of a fluke or if there's some reason it won't work in general.

> Then again, maybe scanner wouldn't work because it would see just
> the new volume label and nothing after that? If so, then when NW
> backs up data to the tape, how does it get past the header?

It forwards past it.  You can read any data up to the last write (which
will be the label itself).  You can write data at that point and
forward.  

> I have a tape - and no real big deal as it was data that could be
> recycled - but I canceled the label operation part way (on the
> snode), but not before it updated the media db. However, the label
> operation got hung and issued errors like: DRIVE_STATUS_NEED_INIT.
> Attempts to inventory, mount or unload the tape failed - after a
> lengthy wait - and finally reported '-' as the volume name, but the
> media db does report the new volume and no longer the previous one.
> But I guess when I canceled the label operation this somehow
> confused NW, and it froze up, unwilling to respond to any commands.
> I finally had to manually eject the tape and put another blank tape
> in the drive and restart NW on the snode to get it to unload the
> darn tape and reset everything properly.
> 
> 2. If I still want to reuse this tape, should I just manually load
> the tape, tar or 'dd' some data to it and then re-label it again
> with NW? How can I get NW to play nice with the tape now given that
> the label operation obviously didn't complete correctly the first
> time?

NW should have no problems labeling it.  The only problem would be if
you want it to 're-label' (keeping the same volume name).  Don't
bother.  Just delete the records for this (empty) volume and then
label this tape as you want.

-- 
Darren

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