UNIX : how can I recover a corrupt tar file from a tape? Post: 302965073

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Operating Systems Solaris UNIX : how can I recover a corrupt tar file from a tape? Post 302965073 by hicksd8 on Saturday 23rd of January 2016 08:57:07 AM

01-23-2016

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Lots of questions to ask about this.

Do you know for certain that it's a tar tape and not cpio or some other proprietary format?

Sometimes tape formats have a header so use a no rewind 'nr' device to prevent rewinding, stopping the tape where it is, and then try again.

Do you know the blocking factor the tape was written in?
If you're trying to read it raw with dd, trying appending each of bs=512, bs=1024, bs=2048 and bs=4096 to the dd command. Perhaps tar was configured to write a different block factor to what dd is defaulted.

DAT's always know internally (without reference to the O/S) if they are reading junk. The DAT mechanism writes enough checksums (created by the drive) to know when the integrity of the data is compromised.

---------- Post updated at 01:57 PM ---------- Previous update was at 11:57 AM ----------

Other thoughts are:-

also try bs=10240 in case it's written with the commonly used block size of 10k

Was the tape written by this DAT drive? Tape transports can go out of alignment (the posts that guide the tape) so you may well find that if you put the tape into the drive that wrote it, it will read with no problem.

hicksd8

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LEARN ABOUT DEBIAN

dds-dd

dds-dd(1)						      General Commands Manual							 dds-dd(1)

NAME

       dds-dd - tool to read a dds device.

SYNOPSIS

       dds-dd [ -f device ]

DESCRIPTION

       dds-dd  reads  a  dds  tape devices (DAT). Every block is read and written to stdout. A tape with unknown block size or blocks of different
       size can be read.

       The default device is /dev/rmt0, which may be overridden with the environment variable TAPE, which in  turn  may  be  overridden  with  the
       -f device option. The device must be a character special file.

OPTIONS

       -f device
	      Device of the tape archive (default is /dev/rmt0).  Must be a character special file connected to a dds tape device.

       -V,--version
	      Print the version number of mt-dds to stderr and exit immediately.

       --help print some screens of online help with examples through a pager and exit immediately.

EXAMPLES

       Example: Read the tape and make a listing:
		 dds-dd | tar ft -

       Example: Read the tape and make a listing:
		 dds-dd | cpio -it

ENVIRONMENT

       The environment variable TAPE overrides the default tape device /dev/rmt0.

       SEE ALSO
	      dds2tar(1), dds2index(1), mt(1), tar(1)

HISTORY

       This program was created to use it in conjunction with dds2tar.

AUTHOR

       J"org Weule (weule@cs.uni-duesseldorf.de), Phone +49 211 751409.  This software is available at ftp.uni-duesseldorf.de:/pub/unix/apollo

									2.4								 dds-dd(1)