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
string::crc32
CRC32(3pm) User Contributed Perl Documentation CRC32(3pm)
NAME
String::CRC32 - Perl interface for cyclic redundency check generation
SYNOPSIS
use String::CRC32;
$crc = crc32("some string");
$crc = crc32("some string", initvalue);
$somestring = "some string";
$crc = crc32($somestring);
open(SOMEFILE, "location/of/some.file");
$crc = crc32(*SOMEFILE);
close(SOMEFILE);
DESCRIPTION
The CRC32 module calculates CRC sums of 32 bit lenghts. It generates the same CRC values as ZMODEM, PKZIP, PICCHECK and many others.
Despite its name, this module is able to compute the checksum of files as well as strings.
EXAMPLES
$crc = crc32("some string");
results in the same as
$crc = crc32(" string", crc32("some"));
This is useful for subsequent CRC checking of substrings.
You may even check files:
open(SOMEFILE, "location/of/some.file");
$crc = crc32(*SOMEFILE);
close(SOMEFILE);
A init value may also been supplied in the above example.
AUTHOR
Soenke J. Peters <peters__perl@opcenter.de>
Please be so kind as to report any bugs/suggestions to the above address.
COPYRIGHT
CRC algorithm code taken from CRC-32 by Craig Bruce. The module stuff is inspired by a similar perl module called String::CRC by David
Sharnoff & Matthew Dillon. Horst Fickenscher told me that it could be useful to supply an init value to the crc checking function and so I
included this possibility.
The author of this package disclaims all copyrights and releases it into the public domain.
perl v5.14.2 2005-04-04 CRC32(3pm)