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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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SMBTAR(1)							   User Commands							 SMBTAR(1)

NAME
smbtar - shell script for backing up SMB/CIFS shares directly to UNIX tape drives SYNOPSIS
smbtar [-r] [-i] [-a] [-v] {-s server} [-p password] [-x services] [-X] [-N filename] [-b blocksize] [-d directory] [-l loglevel] [-u user] [-t tape] {filenames} DESCRIPTION
This tool is part of the samba(7) suite. smbtar is a very small shell script on top of smbclient(1) which dumps SMB shares directly to tape. OPTIONS
-s server The SMB/CIFS server that the share resides upon. -x service The share name on the server to connect to. The default is "backup". -X Exclude mode. Exclude filenames... from tar create or restore. -d directory Change to initial directory before restoring / backing up files. -v Verbose mode. -p password The password to use to access a share. Default: none -u user The user id to connect as. Default: UNIX login name. -a Reset DOS archive bit mode to indicate file has been archived. -t tape Tape device. May be regular file or tape device. Default: $TAPE environmental variable; if not set, a file called tar.out . -b blocksize Blocking factor. Defaults to 20. See tar(1) for a fuller explanation. -N filename Backup only files newer than filename. Could be used (for example) on a log file to implement incremental backups. -i Incremental mode; tar files are only backed up if they have the archive bit set. The archive bit is reset after each file is read. -r Restore. Files are restored to the share from the tar file. -l log level Log (debug) level. Corresponds to the -d flag of smbclient(1). ENVIRONMENT VARIABLES
The $TAPE variable specifies the default tape device to write to. May be overridden with the -t option. BUGS
The smbtar script has different options from ordinary tar and from smbclient's tar command. CAVEATS
Sites that are more careful about security may not like the way the script handles PC passwords. Backup and restore work on entire shares; should work on file lists. smbtar works best with GNU tar and may not work well with other versions. DIAGNOSTICS
See the DIAGNOSTICS section for the smbclient(1) command. VERSION
This man page is correct for version 3 of the Samba suite. SEE ALSO
smbd(8), smbclient(1), smb.conf(5). AUTHOR
The original Samba software and related utilities were created by Andrew Tridgell. Samba is now developed by the Samba Team as an Open Source project similar to the way the Linux kernel is developed. Ricky Poulten wrote the tar extension and this man page. The smbtar script was heavily rewritten and improved by Martin Kraemer. Many thanks to everyone who suggested extensions, improvements, bug fixes, etc. The man page sources were converted to YODL format (another excellent piece of Open Source software, available at ftp://ftp.icce.rug.nl/pub/unix/) and updated for the Samba 2.0 release by Jeremy Allison. The conversion to DocBook for Samba 2.2 was done by Gerald Carter. The conversion to DocBook XML 4.2 for Samba 3.0 was done by Alexander Bokovoy. Samba 3.5 06/18/2010 SMBTAR(1)
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