Linux – Is it possible to open Tar tape on Windows machine

Backup tapes work a little bit differently than your average read-write media . They typically contain proprietary information regarding their format and the data. You usually need to use a program that can understand this format to recover the data -- rather than just "read" from the tape as you might a CDRom or Harddrive with Windows Explorer.

To recover the files contained within your backup set from the tape, you will need to use NTBackup (or Veritas BackupExec, which can read NTBackup files). You will not directly be able to restore from tape to a BKF format that you may be familiar with NTBackup using for backup to disk scenarios.

The data that is written to tape actually is stored in Microsoft Tape Format (MTF), so any software that can read MTF can recover your data.

I'm using this script:

#!/bin/sh

TAPE="/dev/nst0"
mt-st -f $TAPE setblk 0
mt-st -f $TAPE status
totalsize=$(du -csb . | tail -1 | cut -f1)
tar cf - . | \
        gpg --encrypt --recipient target@key.here --compress-algo none | \
        pipemeter -s $totalsize -a -b 256K -l | \
        mbuffer -m 3G -P 95% -s 256k -f -o $TAPE \
                -A "echo next tape; mt-st -f $TAPE eject ; read a < /dev/tty"

To adapt it for your needs, here are the main points:

• tar reads from the current directory and outputs to stdout. This way tar doesn't deal with changing tapes or encryption.
• gpg has compression switched off as this slows the process considerably (100MB/sec+ down to 5MB/sec)
• pipemeter is used to monitor the process and give an estimated time until all the data has been written to tape - this can be removed if it is not needed
• mbuffer buffers the data into memory - this example uses a 3GB buffer, adjust as needed - to allow the tape drive to run for longer before running out of data, reducing "shoe shining" of the tape.
• The -A option of mbuffer handles multiple tapes by ejecting a tape once the end has been reached and waiting for the Enter key to be pressed after the next tape has been loaded. This is where your /root/advancetape script can go.

One issue to be aware of when using this with LTO tapes:

• The tape block size is set to variable, and mbuffer writes in 256k blocks. This works well for me with an LTO3 drive, however tar likes to use a different block size. This, combined with the fact that mbuffer handles the spanning across tapes rather than tar, means you will need to read the data off the tape again through mbuffer and then pass it through gpg and on to tar. If you try to extract it directly off the tape with tar (even if you skipped encryption) it will likely not work, and will certainly break once it reaches the end of the first tape, without giving you a chance to change to the next tape.