The main thing to note about tbackup and tape drives is that tbackup
is not a tape device driver. Tbackup assumes you have a device driver
that can reliably access your tape drive under Linux. If you can't
use your tape drive with normal tools like tar
and
cpio
, you won't be able to do so with tbackup either.
As I don't have a tape drive myself, I can't answer many questions about tape drives or tape drivers. Only ask me if your tape drive works with tools like tar and cpio, but fails to work with tbackup.
Tbackup isn't better at low level tape handling than plain tar, cpio and afio are. It provides no sophisticated recovery procedures for tape errors. It does however add high level directory set and incremental backup facilities. This makes tbackup very convenient to use in a hybrid situation where you do full backups to tapes and incremental backups to floppies. If you never plan to use floppies, but only tapes, you may want to look at other backup packages which offer more tape-specific functionality.
Before you can use your tape drive, the tape device name and
optionally some other parameters need to be configured by editing the
file /etc/tbackup/Config
. The comments in
/etc/tbackup/Config
explain the configuration.
An archive on tape can have error correcting codes added. If a tape has read errors, error correcting codes will often allow reconstruction of the damaged data.
Tbackup has a built-in error correcting code generator for floppies, but no built-in correcting code generator for tapes. However,
ecc
to add error
correcting codesIf you want error correcting codes, first search your documentation to find out if 1) or 2) above apply to your machine. Many modern tape drives that do automatic compression also add error correcting codes.
If case 2) applies, you must switch on the error correcting codes
option before starting tbackup. You will probably also need to
switch them on before running trestore
or another program that
reads the tape, though in some cases this may happen automatically.
In case 3), if your tape drive does not support error correcting codes
directly, you may want to use the ecc
program to add them.
However, this has a few disadvantages:
ecc
whenever the archive is read, the
archive is unreadable without ecc
. In particular, this means
that you can't do a restore without having ecc
. The ecc
program will run on most unix machines, but I don't think there is a
DOS version. This may be a problem if you want to
get files from your backups and have no working Linux machine
available. You may want to make sure that you have access to at least
one other machine/operating system that can read your tapes and run
ecc
.
ecc
program uses lots of CPU time. On a 486/33,
ecc
takes 1 hour of CPU time for every 100 megabyte. Thus, using
ecc
may significantly slow down your backup if you have a fast
tape drive, or even if you have a slow tape drive.
ecc
may give a false sense of safety. Your tape
drive may be of a type that does not benefit much, or benefit at all,
from the particular kind of error correcting codes made by GNU
ecc
. See your tape manual and the ecc
manual page for more
details.
You can find GNU ecc
on most FTP sites that have the GNU stuff.
If you install it, make sure it is in your PATH
so that
tbackup can find it.
If you add error correcting codes to a tape backup using 2) or 3), make a note of it somewhere, because you will need to know the archive has them when restoring the backup.
Adding tape error correcting codes can never do any harm, though it will make the archive a bit larger. Error correcting codes can never fix all possible tape errors; adding them does not mean it is save to omit a tape verify.
Tbackup provides the tape method for reading and writing to the tape drive. Note that this method does not write any information about the backup (contents, pack method used, creation date, ...) on the tape, you will have to record this information yourself.
Here is a sample transcript:
Available write methods:
1 floppy -- write to msdos floppy disks with mtools
2 filedev -- write archive to file or device
3 tape -- write to tape
4 null -- copy archive to the bit bucket
Enter method name or number ---> [floppy] tape
^^^^
Use tape error correcting codes made by GNU ecc?---> (y/n) [n] y
^
[....]
Tape size is 250m.
Is the tape /dev/tape1 ready for writing? Press enter to begin.
Tbackup knows nothing about rewinding or positioning of tapes. You
will have to prepare the tape drive for writing yourself (e.g. be
using a program like mt
) before running tbackup (or at least
before pressing enter).
If the archive length exceeds the tape size you will be prompted for a second tape:
afio: "/dev/tape1" [offset 0]: Output limit reached
afio: Ready for disk 2 on /dev/tape1
afio: quit to abort, anything else to proceed.
(Please ignore the part about being ready for disk 2.) You will see
afio:
in this prompt even if you use the tar pack method.
Tbackup will report tape write errors to you if the tape driver reports them to tbackup. With some tape drivers a tape write error may only produce a kernel message, not a message to tbackup. It may be necessary to watch the kernel messages for errors when writing to tape. (Consult your tape driver documentation, if it exists.)
Once you have written a tape, you may want to verify it for write errors. Tbackup supports two ways of doing this:
tverify
.
tlist
.The first way is safest, it will check the integrity of all data on
the tape. However, this tverify
supposes that the file system
contents did not change during or between the backup and the verify
pass. If a files in the filesystem and on tape are not identical,
tverify
supposes that the copy on tape was written incorrectly.
This may lead to incorrect error reports when verifying against a live
filesystem.
Running tlist
on the tape will verify that the tape data is
readable, and will detect some kinds of archive damage. You may want
to look at the kernel error messages from the tape driver while
running tlist
, these may indicate damage. After running
tlist
, you can check the index file produced for error messages
from the archiver, or compare it against the backup index file.
See the section
tverify
(Running tverify) on tverify
and section
tlist
(Running tlist) on tlist
for more
information on using these commands.
If you have a tape drive, you may want to do backups noninteractively,
e.g. at night. Tbackup has an experimental `batch mode' feature for
scheduling backups as at
or crontab
jobs. See the
documentation file /usr/lib/tbackup/README.batchmode.txt
for
more information.
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