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# 3.3 Backing Up Your Files to CD/DVD

By combining DropDMG’s imaging and burning features, you can easily back up your files to CD-R/RW, DVD-R/RW, or Blu-ray. DropDMG will store the files efficiently on the discs, and you can optionally protect them using encryption.

1. Go to the Configurations tab of DropDMG’s Preferences window and click the + button to make a new configuration. Set the options that you want to use for the backup. Probably you’ll want one of the compressed `.dmg` formats. For an encrypted backup, choose an encryption level and set a passphrase. Use the Sizes pop-down menu to set the size of the segments to match the discs you’ll be using. If you will be backing up an entire disk, make sure that Optimize for restores is checked.

   Note: Since you created a new configuration, you can skip this step next time; just make sure that the proper configuration is selected.

2. To back up a folder, drag it onto the DropDMG window or use one of the other methods. DropDMG will create a `.dmg` and (if necessary) some `.dmgpart` files.

3. Use the Burn… command to burn the `.dmg` and `.dmgpart` files to disc, making sure that it’s set to Burn disk images as files.

4. After the burning is complete, you can delete the `.dmg` and `.dmgpart` files.

This backup method has a variety of advantages over ultra-simple backup methods (e.g. Burn Folders in the Finder) and more specialized backup programs:

- Collecting the files onto a `.dmg` file is better than burning the files directly:

  - The `.dmg` file can be compressed (to save space) and encrypted (to keep your off-site backup private).
  - The `.dmg` file has an internal checksum. When you mount the disk image or use DropDMG’s Verify Image… command, macOS verifies that the backup disc is not damaged. This lets you ensure that your backup remains valid and that the files can be restored correctly.
  - You can easily backup large files that don’t fit on a single CD or DVD because DropDMG will save them into disc-sized `.dmgpart` files.
  - All file ownership and permissions metadata is preserved.

- Backups created with DropDMG are stored in a standard macOS format. The software needed to restore them is built into the operating system.

- The two-step process (creating the disk image files and then burning them) saves time. If you were using software such as Retrospect to back up a large folder, it would prompt you for discs as it copied the files. Then, when it was done, it would prompt you for all the discs again to verify them. During this time, you would not be able to modify the files in the folder, because the backup could be corrupted if you modified files that were in the midst of being copied. Thus, the amount of time that your Mac is “out of commission” is determined by the time it takes to do the burning and swap all the discs.

  With DropDMG, the first step of creating the `.dmg` files can run unattended, while you’re at lunch or sleeping. When you get back to your Mac, you can burn the files to disc at your leisure. Since the folder has already been “snapshotted” to the disk image, you can access and modify the folder while burning the discs. Furthermore, if you have multiple optical drives you can save time by burning multiple discs at a time. Since each disc is verified individually, right after it’s burned, you don’t have to swap the discs twice.

The Restoring Files and Disks section describes how to restore your backup.

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