Does tar do crc checking on a tape or tar file?

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Top Forums UNIX for Advanced & Expert Users Does tar do crc checking on a tape or tar file?
# 1  
Old 05-04-2006
Does tar do crc checking on a tape or tar file?

Trying to answer a question about whether tar table-of-contents is a good tool for verifying tape data.
# 2  
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:
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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