The Evolution of Mac Cloning
For decades, Mac system administrators relied on third-party tools like Carbon Copy Cloner or SuperDuper! to create exact, bootable duplicates of macOS hard drives. This was essential for mass-deploying a standardized system image to fifty iMacs in a computer lab, or for creating a perfect backup before a major OS upgrade.
However, when Apple introduced the Apple File System (APFS) and tightened security with the T2 Security Chip and Apple Silicon, traditional block-level cloning became incredibly difficult. APFS uses complex internal structures like “containers” and “volumes” that don’t map cleanly to older cloning methods.
To safely and reliably clone a modern APFS volume, you should use Apple’s native, built-in command-line tool: asr (Apple Software Restore).
Understanding the asr Command
The asr command is an incredibly powerful, low-level tool that works directly with the APFS architecture. It does not just copy files; it replicates the entire file system structure, including snapshots, metadata, and cryptographic hashes, ensuring the resulting clone is a mathematically perfect copy.
Warning: asr is a destructive command. The destination drive will be completely erased without warning before the cloning begins. Ensure you have selected the correct target disk.
Step 1: Identifying Your Source and Target Volumes
Before you run the command, you need to know the exact disk identifiers for both the drive you are copying from (Source) and the drive you are copying to (Target).
- Connect your external target drive to the Mac.
- Open Terminal (Applications > Utilities).
- Type
diskutil listand press Enter.
You will see a list of all connected drives. Look for the names of your volumes. You need to note the identifier in the far-right column, which looks like disk1s1 or disk3s2.
- Source Identifier: Let’s assume your internal Mac drive is
disk1s1. - Target Identifier: Let’s assume your external SSD is
disk3s1.
Step 2: Executing the Clone
The basic syntax for the asr command requires root privileges (sudo), the source flag (--source), the target flag (--target), and the erase flag (--erase) to prepare the destination.
In Terminal, run the following command, replacing the disk identifiers with your actual values:
sudo asr restore --source /dev/disk1s1 --target /dev/disk3s1 --erase
Step 3: The Restoration Process
Once you hit Enter and provide your administrator password, asr will begin the cloning process. You will see several phases output in the terminal:
- Validating target: Ensuring the destination is a valid APFS container.
- Erasing target: Completely wiping the destination drive.
- Restoring: The actual block-level copying of data. This will display a percentage counter (10%… 20%… etc.) and will take the longest amount of time, depending on the speed of your drives.
- Verifying:
asrperforms a cryptographic check to guarantee the clone is identical to the source. - Inverting target volume: Finalizing the APFS volume structure.
Troubleshooting APFS Quirks
Modern macOS uses a “Volume Group” structure, separating the read-only System volume from the read-write Data volume. If you are attempting to clone a bootable macOS drive, you must target the entire Volume Group, not just the Data volume.
If you encounter an error stating “Could not recognize source as an APFS volume,” you may need to point the --source flag to the actual mount point rather than the raw device identifier, like this:
sudo asr restore --source /Volumes/Macintosh\ HD --target /dev/disk3s1 --erase
When the command finishes successfully, your target drive will be a perfect, bit-for-bit clone of your original APFS volume, ready for backup storage or deployment.