How To Copy a Dual Boot Hard Drive To a Smaller Drive Using DD

Using dd to copy a dual-boot hard drive to a smaller drive can be tricky. The dd command copies data bit-by-bit, including the boot sectors, file systems, and partition table. However, it does not handle resizing partitions, so if your target drive is smaller than the source drive, you will need to shrink partitions manually or use other tools before using dd.

This guide assumes that the dual boot system has Windows and Linux (GRUB as the bootloader), and we will outline the steps for using dd to clone the entire hard drive, including both operating systems, and fix any issues related to resizing partitions afterward.

Step 1: Prepare the New (Smaller) Drive

1. Connect the new (smaller) drive to your system via SATA or USB (using a USB-to-SATA adapter if necessary).
2. Ensure the new drive is unallocated (i.e., no partitions or data on it). If it has any partitions, delete them using gparted or any other partition tool, as we will be copying everything from the source drive.

Step 2: Backup Data (Important)

1. Backup your data from both Windows and Linux to an external drive or cloud storage.
2. Using dd can overwrite the destination drive completely, so make sure everything important is backed up.

Step 3: Boot into a Live Linux Environment

You will need to use a live Linux environment (such as an Ubuntu live USB) to perform the cloning operation.

1. Create a bootable USB with a Linux distribution (e.g., Ubuntu).
2. Insert the USB and boot your computer from it.

Step 4: Identify the Source and Destination Drives

Once booted into the live Linux environment, open a terminal.

Use lsblk or fdisk -l to identify the source drive (the original dual-boot drive) and the destination drive (the new, smaller drive).
Lsblk

 Example output:
NAME   MAJ:MIN RM   SIZE RO TYPE MOUNTPOINT

sda      8:0    0   500G  0 disk 

├─sda1   8:1    0   100G  0 part /mnt/windows

├─sda2   8:2    0   400G  0 part /mnt/linux

sdb      8:16   0   250G  0 disk

In this example:

• /dev/sda is the source (original drive, 500GB).
  
• /dev/sdb is the destination (new drive, 250GB).
  

Make sure the destination drive (/dev/sdb) is unmounted if it is mounted, using umount if needed:
sudo umount /dev/sdb*

Step 5: Use dd to Copy the Entire Disk

Now we will copy the entire disk from the source to the destination drive using dd. This will copy the partitions, boot sectors, and everything else.

Run the dd command to copy the entire source drive to the destination. Be careful with the dd command, as selecting the wrong source or destination drive can result in data loss.

Use the following command:
sudo dd if=/dev/sda of=/dev/sdb bs=64K status=progress

• if=/dev/sda: The source drive (original dual-boot drive).
• of=/dev/sdb: The destination drive (new, smaller drive).
• bs=64K: Set the block size to 64KB for faster copying (you can also use bs=4M for even faster copying depending on your system).
• status=progress: Displays the progress of the copying process.

2. Wait for the dd process to finish. Depending on the size of your drive, this can take several hours.
   

Step 6: Resize the Partitions on the New Drive (If Necessary)

After cloning the drive with dd, you may need to resize the partitions on the new drive to fit the available space. Since dd does a bit-by-bit copy, it does not automatically shrink partitions to fit smaller drives. You will need to resize the partitions manually.

1. Boot into a Live Linux environment (if not already there).
2. Open GParted (or another partition manager).
3. Resize the partitions on the new drive (/dev/sdb) to fit the available space.
   • You may need to shrink the Linux partition and Windows partition, but ensure you leave enough space for both systems.
     
   • Resize the partitions carefully to avoid data loss. It’s important to leave enough room for both operating systems and the bootloader.
4. Apply the changes.
   

Step 7: Reinstall or Repair the Bootloader

After cloning the disk and resizing the partitions, you may need to reinstall or repair the bootloader to make sure the system can boot correctly into both operating systems (Linux and Windows).

Repair GRUB (for Linux and Dual Boot)

1. Boot into a live Linux environment (like Ubuntu).
   Open a terminal and mount your Linux root partition from the new drive. Replace /dev/sdb2 with the partition where Linux is installed:
   sudo mount /dev/sdb2 /mnt
2. Mount the necessary filesystems:
   sudo mount –bind /dev /mnt/dev
   sudo mount –bind /proc /mnt/proc
   sudo mount –bind /sys /mnt/sys
3. Chroot into the mounted system:
   sudo chroot /mnt
4. Reinstall GRUB:
   grub-install /dev/sdb  # Replace with the appropriate drive update-grub
5. Exit and unmount:
   exit

sudo umount /mnt/dev /mnt/proc /mnt/sys /mnt

Repair Windows Bootloader (if necessary)

If Windows fails to boot, you may need to repair the Windows bootloader.

1. Boot from a Windows installation media (USB or CD).
   
2. Choose Repair your computer > Troubleshoot > Advanced options > Command Prompt.

In the command prompt, enter the following commands to repair the Windows 

bootloader:
bootrec /fixmbr

bootrec /fixboot

bootrec /rebuildbcd

3. Restart the system and check if Windows boots.
   

Step 8: Test the Dual-Boot System

1. Restart the system and check that both Windows and Linux boot properly.
2. You should now have a cloned dual-boot setup on the smaller drive.

Optional: Reboot and Recheck Boot Menu

If GRUB doesn’t show up or you have issues with the boot menu, you might need to adjust the boot sequence or ensure that your BIOS/UEFI is correctly configured to boot from the new drive.

Conclusion

By following these steps, you should have successfully cloned your dual-boot hard drive to a smaller drive using dd. The process involves copying the disk byte-by-byte, resizing the partitions if necessary, and ensuring that both the GRUB and Windows bootloaders are properly configured to handle the dual boot setup.

Always remember to back up your data before starting, as partitioning and bootloader management can be risky.