topic Re: How to recover overwrite tape in Operating System - HP-UX

How to recover overwrite tape

Samboja — Mon, 05 May 2003 03:56:52 GMT

Dear all,

I need Ur help.
I've just overwriten tape by tar command. Now I need old data on that tape. Is it possible for me to get old data ?

Thanks for your help.

BR,

Sam.

Re: How to recover overwrite tape

Suhas_2 — Mon, 05 May 2003 03:58:49 GMT

Sam,
To my knowledge, the old data is gone forever.

Rgds..
Suhas

Re: How to recover overwrite tape

Michael Tully — Mon, 05 May 2003 04:09:30 GMT

Sorry, but the data is gone. by default, tar starts at the beginning of the tape.

Re: How to recover overwrite tape

Eugeny Brychkov — Mon, 05 May 2003 04:18:33 GMT

Sam,
try http://www.vogon-international.com . Data overwritten is lost, but I believe if there's a data chunk left from that backup (not overwritten but your tar operation) then something can be saved
Eugeny

Re: How to recover overwrite tape

John Bolene — Mon, 05 May 2003 11:31:01 GMT

If you did not overwrite all of the tape, then one of the data recovery companies might be able to recover what was not overwritten, but be aware that these companies charge a premium for their services, to the tune of thousands.

It depends on what the data is worth.

Otherwise, consider that you have made a mistake and it is not recoverable.

Re: How to recover overwrite tape

Mark Greene_1 — Mon, 05 May 2003 11:44:21 GMT

If the tar didn't write over the whole tape, you may be able to skip past the tar with mt & the fsf option to get to the remainder of the old save, and then pull what's left off the tape with dd.

HTH
mark

Re: How to recover overwrite tape

Shannon Petry — Mon, 05 May 2003 11:54:14 GMT

This is a specialized companies job. We had a similar thing occur about 5 years ago, we found a company out in CA which could extract all of the volumes from the tape. However, this takes special hardware and software to do. Here is the basic's of why...

When you write to a tape, there is a EOF mark maded, then an EOM mark. When you do something like this..

tar cvf /dev/rmt/0mn /etc

/etc is put on tape, and an EOM mark is written (2 EOF marks).

Now, since we did not rewind the tape, we can do this...

tar cvf /dev/rmt/0m /usr

Now, the last EOF mark is erased and the new volume created. Remember that EOM is a double EOF, so we still have 1. The new volume is written, then a new EOM mark is made. *NOTE I REWOUND THE TAPE*

Now, we do this.

tar cvf /dev/rmt/0mn /etc

The tape has been rewound, and now we have created a new volume of /etc. A new EOM mark is made. Our backup of /usr is now gone, as we can tell the tape to go to an EOF mark, or an EOM mark. There is no way with standard hardware to pass an EOM mark.

Hope this helps explain it all :)

Shannon