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