Creating a full, bootable backup of a USB drive as an .iso or .img file is a critical task for IT professionals and tech enthusiasts. Whether I am archiving a custom Windows installer, preserving a Linux live environment, or creating deployment images, a sector-by-sector clone ensures that the bootloader, partition table, and all data are perfectly preserved.

This guide provides three reliable methods to clone a bootable USB drive, catering to different user preferences: the command-line power of PowerShell with WSL, the simplicity of a GUI tool on Windows, and the classic dd command on Linux.

💡 Why Create an ISO from a Bootable USB?

A bootable USB is more than just a collection of files; it contains a specific structure that allows a computer to boot from it. This includes:

  • A partition table (either MBR or GPT) that defines the layout of the drive.
  • Boot sectors that contain the initial code to start the boot process.
  • One or more partitions formatted with a specific file system (e.g., FAT32, NTFS, or exFAT).

When I clone the device into an ISO or IMG file, I am creating a sector-by-sector image of the entire drive. This preserves the complete boot structure, ensuring that the backup can be restored to another USB drive and remain bootable.

🪟 Method 1: Using PowerShell with WSL (Recommended for Power Users)

For users comfortable with the command line, using the Windows Subsystem for Linux (WSL) provides access to the powerful dd utility, a standard tool for creating raw disk images on Linux. This method is fast, scriptable, and requires no third-party software.

Step 1: Identify My USB Drive in PowerShell

First, I needed to identify the disk number of my USB drive. I opened PowerShell as an Administrator and ran:

Get-Disk

I looked for my USB drive in the output and noted its Number.

Number Friendly Name  OperationalStatus Total Size Partition Style
------ -------------  ----------------- ---------- ---------------
0      NVMe SSD       Online            512 GB     GPT
1      USB DISK 3.0   Online            16 GB      MBR

In this example, the USB drive is Disk 1.

Step 2: Identify the Device in WSL

Next, I opened my WSL terminal (e.g., Ubuntu) and listed the available block devices to find the corresponding Linux device path.

sudo fdisk -l

I saw output similar to this, where /dev/sdb corresponded to my USB drive.

Disk /dev/sda: 512 GiB, 549755813888 bytes, 1073741824 sectors
...
Disk /dev/sdb: 14.9 GiB, 16008609792 bytes, 31266816 sectors
...

⚠️ I made absolutely sure I identified the correct device. Using the wrong device name in the next step can lead to data loss.

Step 3: Clone the USB to an ISO File

Now, from my PowerShell terminal, I used wsl to execute the dd command. This command read from the USB device (/dev/sdb) and wrote to an ISO file on my Windows file system.

wsl sudo dd if=/dev/sdb of=/mnt/c/Users/$env:USERNAME/usb_backup.iso bs=4M status=progress

Command Explanation:

  • wsl sudo dd: Executes the dd command with administrative privileges inside WSL.
  • if=/dev/sdb: Specifies the input file (my source USB drive).
  • of=/mnt/c/...: Specifies the output file path. /mnt/c/ is how WSL accesses my C: drive.
  • bs=4M: Sets the block size to 4MB for faster copying.
  • status=progress: Shows the live progress of the copy operation.

When the command completed, I had a bootable usb_backup.iso file in my user directory.

Step 4: Restore the ISO to a USB (When Needed)

I could later use the same dd command to write the ISO image back to a new USB drive.

wsl sudo dd if=/mnt/c/Users/$env:USERNAME/usb_backup.iso of=/dev/sdb bs=4M status=progress
wsl sync

💿 Method 2: Using a GUI Tool (Win32DiskImager)

If I preferred a graphical interface, Win32DiskImager is a popular, free, and open-source tool that makes disk imaging simple and safe.

Step 1: Download and Install

  1. Download Win32DiskImager from the official SourceForge repository.
  2. Install the application and run it as an Administrator.

Step 2: Read the USB to an Image File

  1. Device: I selected my USB drive from the dropdown list (e.g., [E:\]). Be extremely careful to select the correct drive.
  2. Image File: I clicked the folder icon and chose a location and filename for my backup (e.g., C:\Users\YourUser\Desktop\usb_backup.img). Win32DiskImager uses the .img extension by default, which is functionally identical to .iso for raw disk images.
  3. Read: I clicked the Read button. This copied the entire USB drive, sector by sector, into the image file I specified.

To Restore: I could later use the Write button to restore this image file to the same or a different USB drive.

🐧 Method 3: Using Linux Directly

If I was working on a Linux machine, the process was even more straightforward.

Step 1: Identify the Device I used lsblk or fdisk to identify my USB device path (e.g., /dev/sdb).

sudo fdisk -l

Step 2: Clone to ISO I used the dd command to create the image.

sudo dd if=/dev/sdb of=~/usb_backup.iso bs=4M status=progress
sync

The sync command ensures that all write caches are flushed to the disk.

🤔 Which Method Should I Choose?

Method Best For Pros Cons
PowerShell + WSL Power users, automation, scripting No third-party tools needed, fast, scriptable Requires WSL and command-line knowledge
Win32DiskImager (GUI) Beginners, users who prefer a graphical interface Safe and easy to use, clear UI Requires downloading and installing a third-party tool
Linux dd Native Linux users The standard and most direct method on Linux Requires a Linux environment

🚀 Conclusion

Cloning a bootable USB drive is a simple process once I had the right tools.

  • For Windows power users, combining PowerShell and WSL offers a fast, native, and scriptable solution without needing to install any third-party software.
  • For those who prefer a safer, graphical approach, Win32DiskImager is an excellent and reliable choice.
  • For Linux users, the native dd command remains the gold standard.

By creating a full disk image, I could ensure that I always had a perfect, bootable copy of my important USB drives.