Date: Sun, 7 Sep 1997 10:45:28 +0200 From: j@uriah.heep.sax.de (J Wunsch) To: freebsd-hackers@FreeBSD.ORG Cc: gmarco@giovannelli.it (Gianmarco Giovannelli) Subject: Re: a c at the place of x (tar error) Message-ID: <19970907104528.OH62321@uriah.heep.sax.de> In-Reply-To: <199709030529.AAA01636@argus.tfs.net>; from Jim Bryant on Sep 3, 1997 00:29:13 -0500 References: <19970903133610.20557@lemis.com> <199709030529.AAA01636@argus.tfs.net>
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As Jim Bryant wrote: > i think that if a formal survey were done, nobody has made this > mistake [heh, heh], but then you are one of the brave few who have > admitted to such braindeath [we all should be so brave]. > > try this: > > tar -tvzf /dev/nr[sw]t[0-7] > > that will skip past the "oops" archive. > > next > > use dd to get the remainder of the damaged archive. > > next Sheesh! You should at least have a little knowledge about tape drives before posting... Your suggestion won't work. EOM (``end of recorded medium'', as the SCSI specs call it) is a condition that is caught inside the drive itself. You can't position a tape behind this spot as long as the tape's firmware adheres to the SCSI specs. (Companies specializing on data recovery are said to have drives with patched firmware for just this purpose.) The only trick that, as rude as it sounds, would work is the following: Start writing some archive to the tape (preferrably some junk that doesn't interfere with the data you're going to recover, but don't just write NULs since programs like tar(1) might misinterpret them as the end of their archive). Just after this process started, turn off the power of the tape drive(!). This prevents the drive's firmware from recording the EOM mark that it would normally add. Now, turn power on again, rewind the tape, try skipping the junk you've just written (which must have been large enough to clobber the previous EOM mark), and try to make some sense out of the data that became visible again. Seriously, getting used to always write-protect your tapes after taking them out of the drive is the simpler method... -- cheers, J"org joerg_wunsch@uriah.heep.sax.de -- http://www.sax.de/~joerg/ -- NIC: JW11-RIPE Never trust an operating system you don't have sources for. ;-)
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