2 Introduction

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Tbackup (three backup) is a user friendly, fault tolerant package for making backups of a Linux filesystem. It is primarily designed to make multi-megabyte backups to a set of floppy disks. It has incremental backups, backup indexes, selective restore, error correcting codes, and more.

2.1 Why not use tar or cpio?

Archiver programs such as tar, cpio and afio also allow you to make backups to floppy disks. But tar stands for tape archiver, it was not designed for the specific problems you can have with floppies.

If you back up 100 megabytes to some 50 floppies with tar, several things can go wrong:

  1. disk 40 has a bad sector that can't be written to
  2. disk 41 was not formatted
  3. you forgot to insert disk 45 and pressed enter with disk 44 in the drive

tar was not designed to handle such conditions gracefully. It will abort on errors 1 and 2, and will not warn you about 3. The only way to correct these errors is to start over again at disk 1, and that is hardly acceptable.

Tbackup was designed to recover from all the errors above (and a lot more).

For small backups of say less than 5 floppy disks you can just as well use tar or cpio (it is even slightly faster than tbackup), but for big backups tbackup is better.

Also, tbackup includes backup management functions not found in programs like tar and cpio.

2.2 Fault tolerant archive format

Being able to quickly recover from errors when an archive is created is nice, but not the most important aspect of a backup package.

It is the restore that really matters. Like hard disks, the floppies or tapes used for a backup can develop bad spots and give read errors. If this happens, the restore program should still be able to recover as much information as possible.

If you use tar (with some auxiliary program like disksplit) to make compressed archives on a set of floppy disks, even a single read error is disastrous. If one sector on disk 5 is damaged, you not only loose a part of disk 5, ALL information on disks 6-50 will also be lost. Compressed tar archives on tapes have the same problem.

Tbackup makes a fault tolerant kind of compressed archive: only the the files in the archive are compressed, the file headers are left uncompressed. This way, a read error generally only causes the loss of one or two files.

If floppy disks are used for the backup, tbackup can add error correcting codes to the data on the floppy. If a floppy then develops bad spots, the restore program can often reconstruct the missing data using the error correcting codes. This way the the entire archive can be restored even if there are some read errors.

2.3 Other advantages

Apart from the error recovery mechanisms, tbackup has some other advantages.

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