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32 Posts
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7214
July 25th, 2017 14:00
Networker - Recover backup data from a tape that was relabeled.
Dear all,
I hope somebody could help us to recover a tape volume (LTO6) with valid backup data that was accidentally relabeled (within the same pool but using a different barcode***).
We have tried a "scanner -n -S xxxxx /drive_0", to see if the savesets saved with the old label are still readable but, no "luck".
The tape volume was not used to save any new or further data so, the problem is, as far as I understand, the new EOD mark (End of Data) that the volume has due to the relabel action.
Are there any option/idea on how we can recover the volume/saveset metadata of that tape without:
- perform a mmdb recover (due to bootstrap backup was never performed) ?
As a last resource we can try to recover the data but, correct me if I am wrong, in that case, "uasm directive" will not help, as it depends on scanner command.
*** due to a misunderstanding between Administration team and Operation team, the valid tape was removed from the physical library, physically relabeled with a new barcode label, loaded again in the tape library and performed a relabel action from Networker.
Many, many thanks for all of you that could read and/or help with this issue.
Kind regards.
wlee
263 Posts
1
July 25th, 2017 21:00
When the tape is relabeled, a new tape label is written at the beginning of the tape followed by two EOF marks to signify to the tape drive that it is end of data (EOD). This prevents the tape drive from reading past that point. The information that is actually past EOD is still there. It is just that you cannot get passed the EOD marker, which tells the tape drive that there is nothing after that point. That's why scanner will not see the data that is passed the tape label. Nor any other conventional tape reader software.
Recovering the NetWorker media database will only help you to know what was on that tape. It will not help you to get to the tape. It is the physical hardware that is preventing you from accessing passed that point. Recovering the media database will let the NetWorker server that the backup of client's data is located on tape file position x and record position y. But the hardware will prevent you from moving to that position past file #2 record #0, which is where the next position to write to when a tape is labeled. And this is the starting position where the backup savesets are written to on the tape.
If the data is important and needed, then please set the write protect tab on the tape cartridge. This will at least prevent it from being written to and overwriting the data that is still on the tape.
The following link also talks about the same issue... take a look.
http://www.forensicfocus.com/Forums/viewtopic/t=9781/
In the Dell EMC knowledgebase, there might still be a document that describes a "possible" method of getting past the EOD marker. The document that I remember is more that 15 years old, so not sure if it is available or applicable, but you can still take a look, assuming that I can still find it.
As mentioned in other sources, there are 3rd party companies that specialize in data recovery. So it is possible to get back the data... if you feel the data is worth the money.
One conversation I had with a "specialist" told me that he was able to recover data from a hard drive, even after it was reformatted 7 times.... so there is hope...
bingo.1
2.4K Posts
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July 25th, 2017 22:00
Yes you can - but you must be very careful.
The official solution is to get in touch with a data recovery company (in Europe I would think about Kroll Ontrack or Vogon).
Of course this would be the most expensive method.
The other solution is the 'trial and error method'. This will not cost you anything but you need to understand, at least essentially, ...
- how tape drives work
- about NetWorker's open tape format
- how NetWorker works
I have tested that method and documented the procedure 15 years ago (most likely the document Wallace is refering to).
You can still download it from this location:
ftp://ftp.legato.com/pub/NetWorker/German/tdocs/archive/nw_cookbook_jan_2009.pdf
The information you are interested in starts on page 455.
Now - if you decide to try that I strongly recommend ...
- to install a NW eval machine
- to use a standalone tape drive
- to run the procedure at least 10 times to familarize yourself
And be aware that you at least will lose a certain amount of data at the beginning of tape.
Diego.Palopoli
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32 Posts
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July 31st, 2017 02:00
Wallace, thank you very much for your detailed and accurate explanation.
Great point about it will be useless to recover mmdb (in case it would be available), I did not notice that would not help.
I will let you know in case we can recover the data, and the method involved.
Diego.Palopoli
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32 Posts
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July 31st, 2017 02:00
bingo, I really appreciate your amazing help.
I have checked the pages you remarked and I have surprised myself finding the detailed and clearly explanation for all the steps.
Last, but not least, thanks a lot also for sharing the rest of all your work, your documentation efforts were more than exceptional!
I will ask permission to follow those steps and try to recover the data, and I also will let you know if I get succeed.
bingo.1
2.4K Posts
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July 31st, 2017 04:00
Hi Diego,
thanks for your appreciation. It also shows that NetWorker has not really changed in core behaviour over all these years.
It has just improved ;-) .
Wankserty
2 Posts
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September 5th, 2017 03:00
To recover backup data from a tape ?
Sorry , i have never tried it , but this seems to be the same thing with phone backup recovery , to recover the backup data , you just need to know how to enter into the backup files , and scan it to get more data from backup files, only in this way , you can recover data from backup , who has other supplements
ble1
2 Intern
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14.3K Posts
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September 5th, 2017 04:00
It can be done... bingo described one way. I remember some 15 years ago we had couple of customers at company I was at where they had the same need... and to do it they had to talk to companies which had specialized libraries with modified drives that would "ignore" EOD marker. From there they could restore data back or create another copy with data on it. It was also a bit expensive, but who needs it will do it anyway. Normally this companies have enough knowledge of major backup products and know their way around it so your own input is kept at minimum.