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The question involves HP LTO Ultrium-4 ( HP C7974A - 800/1.6TB) magnetic tape cartridge. The writing method is TAR.

A while ago, I made a terrible mistake by overwriting the beginning of the tape HP-LTO-4 with 1GB of data. I immediately pressed ^C then I realized the mistake.

The cartridge is almost full - 750GB. The file was intended to be written on file position 250*. I do have to mention that I do know the file position and block number (of each 10th file). The problem is that right now I can not wind to any other position of the tape.

When I want to go to the file nr. 20:

# mt fsf 20

I get:

/dev/nst0: Input/output error

and the status:

# mt status
SCSI 2 tape drive:
File number=1, block number=-1, partition=0.
Tape block size 0 bytes. Density code 0x46 (LTO-4).
Soft error count since last status=0
General status bits on (9010000):
 EOD ONLINE IM_REP_EN

Any advice about that? How do I solve that mistake by winding to the next 10 or 20 positions (assuming that I know the file and block number) and recover the data? Is there any way to write a file until the last known position without doing an EOD?

Thank you in advance.

Giacomo1968
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Ion
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1 Answers1

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Here is an interesting experiment though it is not recommended for everyone.

First of all, once new EOD is written, there is no way for client to let the drive go beyond this position, because it is under control of the drive firmware. Thus, the best option to recover your backup is to call for help to data recovery company, which will be expensive (but the value of your data can be more expensive).

Here is a quote from the webpage above to recover data by yourself:

Overwriting the tape again, with just the right amount of data to clobber the premature EOD marker that was keeping us from reaching our precious backup data. Powering off the tape drive, before it has the chance to write another EOD marker, as it is designed to do

Again, this is a very dangerous way which potentially erases your backup and do it by your own responsibility. Also, I have not tried this way with LTO system. However, the idea is to erase EOD which you have created by mistake. Since the whole procedures are documented in the website, I do not go into detail here.

Kevin Nakamoto
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