How to Configure and Remove a Hyper-V Pass-through Disk

Pass-through Disk Pros and Cons

Whether you are a software developer, an IT professional, or a technology enthusiast, many of you need to run multiple operating systems. Hyper-V lets you run multiple operating systems as virtual machines on Windows.

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In general, the Hyper-V virtual machines can be configured to use one or more virtual hard disks, or a dedicated physical hard disk, which is referred to as a pass-through disk. Some people may like to bind a virtual machine to a pass-through disk because of the following reasons:

• It performs better than virtual hard disks because there is less overhead.
• It uses a simpler storage path because it does not involve the file system on the host.
• It is better aligned with the SAN.
• It can reduce CPU usage.
• It supports large disks.

However, using pass-through disks has some significant disadvantages, which makes you migrate and remove the pass-through disk. The disadvantages include:

• The pass-through disk can only be used by one virtual machine.
• Hyper-V cannot take a snapshot of the pass-through disk. The pass-through disk cannot be backed up by the Hyper-V VSS Writer and the backup program using Hyper-V VSS Writer. This point may limit the use of the Live Migration feature.

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This post tells you how to configure a pass-through disk and how to migrate and remove it. You can try them.

How to Configure a Pass-through Disk in Hyper-V

Step 1: In the host computer, take a disk offline.

• Press “Win + R” keys simultaneously to open the Run
• Enter “msc” in the Run prompt and click OK button to open the Disk Management console.
• Locate the disk that you want to dedicate to the virtual machine. Please make sure that the disk does not contain any volumes.
• Right-click on the disk and choose the Offline command from the shortcut menu.

Step 2: Configuring pass-through disk in Hyper-V Manager.

• Open Hyper-V Manager and go into the Settings for the virtual machine that you plan on linking to the disk.
• Go to the Hard Drive
• Select the Physical Hard Disk
• Select the hard disk that you want to use from the drop-down list.

How to Convert the Pass-through Disk to a Virtual Disk and Remove It

Tip: It’s a good idea to back up the VM before you start in case anything goes wrong. In addition, you should make sure that you have enough free space to create a virtual hard disk that is at least as large as the physical disk that you are replacing.

Step 1: Create a virtual hard disk

• Shut down the virtual machine.
• Open Disk Management on the host machine and note the disk number.
• Open Hyper-V Manager, and select New >Hard Disk under Actions. This will open the New Virtual Hard Disk Wizard.
• Choose the disk format. You should choose the VHDX option unless you have a compelling reason to create a VHD-based disk instead.
• Choose disk types. You will be asked to create a fixed-size, dynamically expanding, or differencing disk. Choose the Dynamically Expanding option and click Next, because it can be difficult to correctly size a fixed-length disk, although Fixed Size option does deliver better overall performance.
• Specify a name and a location for the virtual hard disk that you are creating. Please save the virtual hard disk in a location that has plenty of free space.

Step 2: Replace the pass-through disk with the new virtual disk in the Configure Disk screen.

• When you complete step 1 and click Next, you will be taken to the all-important Configure Disk
• Choose Copy the contents of the specified physical disk, and select the pass-through disk that you plan to replace. The disk number that you noted in Disk Management can help you identify the pass-through disk.
• Click Next again and you will be taken to a summary screen. Take a moment to make sure that the information displayed on the summary screen is correct, and then click Finish to begin the conversion process.

Step 3: Remove the physical disk and bind the virtual hard disk to your VM.

• Go to the virtual machine’s settings.
• Select the physical disk and click the Remove button, followed by the Apply
• Click on the SCSI Controller and select the Hard Disk
• Click the Add button and then choose the Virtual Hard Disk option when prompted.
• Click the Browse button and select the new virtual hard disk that you have created and click OK.