Tutorial: Clone a Disk Over SSH with Compression

This guide explains how to clone a disk (/dev/sda) from a source machine to a destination machine over SSH using dd and gzip for compression.

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Prerequisites

1. Source Machine:

   • Ensure dd, gzip, and ssh are installed.

2. Destination Machine:

   • Ensure gzip and ssh are installed.

3. Network Setup:

   • Both machines should be accessible over the network.
   • You need SSH access to the destination machine.

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Command Overview

The command performs the following:

1. Source Machine:

   • Reads data from the disk (/dev/sda) using dd.
   • Compresses the data using gzip.
   • Sends the compressed data over SSH to the destination machine.

2. Destination Machine:

   • Decompresses the received data using gzip.
   • Writes the decompressed data to its disk (/dev/sda) using dd.

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Command Breakdown

On the Source Machine:

dd if=/dev/sda bs=5M conv=fsync status=progress | gzip -c -9 | ssh user@DestinationIP 'gzip -d | dd of=/dev/sda bs=5M'

• dd if=/dev/sda:
  • Reads the disk (/dev/sda) on the source machine.
• bs=5M:
  • Sets the block size to 5 MB for efficient data transfer.
• conv=fsync:
  • Ensures data integrity by forcing a filesystem sync.
• status=progress:
  • Displays progress while copying.
• gzip -c -9:
  • Compresses the output of dd with maximum compression (-9).
• ssh user@DestinationIP:
  • Sends the compressed data to the destination machine over SSH.
• 'gzip -d | dd of=/dev/sda bs=5M':
  • Decompresses the received data and writes it to the disk (/dev/sda) on the destination machine.

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Steps to Execute

1. Identify the Disks:

   • Use lsblk or fdisk -l to identify the source and destination disks.
   • Example: /dev/sda.

2. Run the Command:

   • Replace user with the SSH username.
   • Replace DestinationIP with the IP address or hostname of the destination machine.
   • Execute the command on the source machine.

3. Monitor Progress:

   • The status=progress option will display the data transfer progress.

4. Verify:

   • Once completed, verify the disk on the destination machine by checking its content or filesystem.

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Example

Source Machine Command:

dd if=/dev/sda bs=5M conv=fsync status=progress | gzip -c -9 | ssh root@192.168.1.100 'gzip -d | dd of=/dev/sda bs=5M'

Explanation:

• Cloning /dev/sda from the source machine.
• Sending data to the destination machine with IP 192.168.1.100.
• Using SSH with the root user.

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Notes

• Data Loss Warning:
  • Be careful with dd as it can overwrite data. Double-check the destination disk path.
• SSH Key Authentication:
  • Use SSH key authentication to avoid being prompted for a password during the process.
• Network Speed:
  • The command's speed depends on network bandwidth and disk I/O.

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Troubleshooting

1. Permission Denied:
   • Ensure proper disk access permissions on both machines.
2. Slow Transfer:
   • Use a larger block size (e.g., bs=10M) to potentially speed up the transfer.

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This command and tutorial provide an efficient way to clone disks across machines securely and with compression.