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Full Discussion: Does tar do crc checking on a tape or tar file?
Top Forums UNIX for Advanced & Expert Users Does tar do crc checking on a tape or tar file? Post 302072600 by Perderabo on Thursday 4th of May 2006 10:09:12 AM
Old 05-04-2006
You are asking two different questions. No, tar, does not do its own crc. Most (perhaps all) modern tape drives will do a crc automaticly, or more likely, something far beyond a mere crc such as a two-level Solomon-Reed ecc. According to a brochure that I have here:
Quote:
DLT technology provides this exceptional data integrity through a multi-layer approach. An application-specific intregrated circuit (ASIC) chip interleaves a Reed Solomon error-correction code of 16KB with every 64KB of user data, a 64-bit cyclic redundancy code (CRC), and a 16-bit error-detection code (EDC) for each 4KB of data, along with an overlapped 16-bit CRC on each user record. As an added safety measure, DLT products verify data by performing a read after each write command, and will automatically re-record data further down the tape if a recording error is detected.
As for the table of contents, it is a fairly good way to verify a tar archive on tape. tar must read to the end of the archive to produce it.
 

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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)
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