Below is a sample Bash script and accompanying guide that demonstrate one way to automate:

1. Creating a single encrypted archive from your data.
2. Splitting that encrypted archive into 100GB chunks.
3. Generating checksums and a manifest/catalog.
4. Optionally creating ISO images from each chunk for more convenient burning.
5. Burning the resulting chunks (or ISOs) to M-Disc.

Important

• This script is written in Bash for Linux/macOS compatibility. It should also work on FreeBSD with minimal (if any) modifications, but you may need to install or adjust the relevant tools.
• The script focuses on automating the encryption and splitting steps, as well as generating a manifest.
• Burning to M-Disc on different platforms can vary. We show an example using growisofs (common on Linux) and hdiutil (macOS). Adjust as needed.
• For best security, do not hardcode your passphrase in the script. You should be prompted for it.

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How to Use the Script

1. Install Dependencies
   Make sure the following tools are installed on your system(s):

   • tar
   • xz
   • gpg
   • split
   • sha256sum (or shasum on FreeBSD/macOS)
   • genisoimage or mkisofs (for creating ISOs if desired)
   • growisofs (Linux) or hdiutil (macOS) for burning.

2. Make the Script Executable

   chmod +x backup2mdisc.sh
   

3. Run the Script

   ./backup2mdisc.sh /path/to/source /path/to/destination 100G --create-iso --burn
   

   • /path/to/source: The directory you want to back up.
   • /path/to/destination: Where to store the intermediate backup files before burning.
   • 100G: The chunk size. Adjust if you're using different capacity discs.
   • --create-iso (optional): Create ISO images from each chunk for more convenient burning.
   • --burn (optional): Attempt to burn each chunk/ISO to disc automatically.

4. Enter Your GPG Passphrase

   • The script will prompt for a passphrase. This passphrase encrypts your data. Keep it safe!

5. Wait for the Script to Finish

   • A large tar + xz + gpg pipeline can take a considerable amount of time depending on your data size.
   • After encryption, it splits into 100GB chunks.
   • It then generates a manifest with SHA-256 checksums of each chunk.

6. Burn to M-Disc

   • If you used --burn, the script will prompt you to insert an M-Disc for each chunk or ISO.
   • On Linux, it uses growisofs. On macOS, it attempts hdiutil if ISO files exist.
   • If you prefer manual burning, skip --burn and burn the .iso files using your favorite tool.

7. Store the Manifest Safely

   • The manifest (backup_manifest.txt) in the work directory includes:
     • Checksums for each chunk.
     • The original source path.
     • Timestamp.
   • Keep this manifest (and the passphrase!) somewhere secure. You'll need all parts to restore.

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Restoring Your Backup

To restore from these discs:

1. Copy all chunk files (or .iso contents) back to a working directory on your system.
2. Combine them back into a single file (if they were split outside of an ISO filesystem, just cat them together):

   cat backup.tar.xz.gpg.* > backup.tar.xz.gpg
   

3. Decrypt and extract:

   gpg --decrypt backup.tar.xz.gpg | xz -d | tar -xvf -
   

   You'll be prompted for the same GPG passphrase. Once it's done, the original files/folders should appear in your current directory.

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Notes & Tips

• Individual Chunk Decryption:
  The above script creates one large encrypted archive, then splits it. You need all parts to decrypt. If you want each 100GB chunk to be decryptable separately, you'd need to tar smaller subsets of data individually, encrypt each, and then burn. This is more complex and requires advanced scripting or a specialized backup tool.

• Automated Backup Tools:
  You might also consider tools like Duplicati, Borg, or restic, which support encryption, deduplication, and chunking. However, writing those chunks onto M-Disc is still a manual step.

• Testing:
  Test with a small directory first (say 1GB) and 100MB “chunks” to ensure your workflow is correct. Then proceed to the full data.

• M-Disc Drive Compatibility:
  Make sure your optical drive explicitly supports writing to 100GB BD-XL M-Disc. Standard Blu-ray or DVD drives often do not support higher-capacity M-Discs.

• Verification:
  Always verify that your burned discs are readable. You can mount them and use the checksums from the manifest to confirm data integrity.

That's it! This script and guide should get you started creating encrypted backups on 100GB M-Discs, with a manifest to track chunks and checksums, plus optional ISO creation and automated burning steps. Adjust as necessary for your specific environment and needs.