System tricks: Windows disk signature conflict and its solution

Cloning a disk or cloning a system is the quickest way to upgrade a disk. However, perhaps when we add a newly cloned hard disk or mount a newly cloned VHD virtual disk in Windows 10, the new disk will show the message “This disk is offline because it has a signature conflict with another online disk” in Disk Manager (Figure 1). So, what is a “signature conflict” on a disk and how to avoid it?


1. About the “signature conflict” of the disk

To understand disk signature conflicts, we must first understand “disk signature”. A disk is an important storage device for saving, transferring and reading data files in a computer system. In order to distinguish storage devices on a computer system, each disk is marked with a uniquely numbered “disk signature”. The unique identifier of the disk signature is stored as part of the disk’s master boot record.

If we clone the contents of an existing hard disk with a newly purchased hard disk and both disks are mounted on the same system for work, or if we create one or more VHD disks through virtual machine cloning and mount them on the same system for work, then we will encounter a signature conflict. Because these simultaneously used disks are copies of the same disk, these copies have the same disk signature, and when used simultaneously, the disk signature conflict problem will be encountered.

2. Handling of signature conflicts on different versions of the system

When two disks have the same disk signature, Windows system does not allow two disks to work at the same time, so a disk signature conflict will occur. So, do different versions of Windows systems handle signature conflicts in the same way?

With older versions of Window such as Windows XP and Vista, signature conflicts usually do not attract our attention because Windows system automatically replaces disk signatures that report having duplicate signatures. However, when using Windows 7, Windows 8 and Windows 10 systems, the situation changes. When two storage devices have the same disk signature, the newly added drive will be closed, offline, and will need to be re-signed before it can be used.

3. Two Ways to Resolve Disk Signature Conflicts

The most convenient way to resolve a disk signature conflict is through Disk Manager. Right-click the Start button and select Disk Management to launch Disk Manager (Figure 2).


In Disk Manager, right-click on the disk marked as offline and select the “Online” option in the menu. When you select the Online option, Windows will generate a new disk signature, which will solve the signature conflict problem (Figure 3).


However, sometimes if you encounter a special situation where you have problems with Disk Manager and cannot access it, you can try using commands to resolve the disk signature conflict. Type “Command Prompt” in Cortana and click “Run as administrator” in the best match search results to launch the Command Prompt window in administrator mode (Figure 4).


Type the diskpart command and enter to run to open the disk management task (Figure 5).


Run the list disk command to display all available disks on the system (Figure 6).


Next, note the number of the problematic disk in the list with the status “offline” and write the command to select the offline disk in the following format

select disk x

where x is the number of the disk with the problem. For example, the select disk 1 command shows disk 1 as the selected disk (Figure 7).


Immediately afterwards, use the uniqueid disk command to display the ID code of the disk signature (Figure 8).


To change the disk signature and set the disk online, type a command like unique disk ID= (New signature). In practice, the (New signature) is replaced with the new ID (hexadecimal number). For example, to set the new ID to unique disk ID=1345ABCD, the command line uses unique disk ID=1345ABCD (Figure 9).


Tip: If the given signature ID is in the wrong format, an error message prompt will be displayed asking to give the ID of the MBR disk in hexadecimal form or the ID of the GPT disk in GUID code form. since the disk in this example uses the traditional MBR format, use the hexadecimal code; if you use the GPT disk format, use the long GUID code string.

After the above command is executed, reboot the system and the disk will be ready for normal use.

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