What is the PortableBaseLayer partition in Windows 10 Disk Management?

After upgrading to Windows 10 version 1903 (19H1), the Disk Management window may display an additional drive named PortableBaseLayer with a capacity of 8191MB (8GB).

Table of Contents

What is PortableBaseLayer appearing in Disk Management?
Is PortableBaseLayer related to Reserved Storage?

When you right-click on the PortableBaseLayer drive, all options (except Properties ) will turn gray.

PortableBaseLayer also appears in the Optimize drives window as a virtual hard drive. You may be wondering exactly what is PortableBaseLayer. The answer will be in the following article.

Picture 1 of What is the PortableBaseLayer partition in Windows 10 Disk Management?

PortableBaseLayer with 8191MB capacity (8GB)

What is PortableBaseLayer appearing in Disk Management?

PortableBaseLayer is not a malicious drive. It is a mounted virtual drive (.vhdx) and used by the Windows Sandbox feature.

If you run a command mountvolfrom the Command Prompt, you can see the GUID volume of PortableBaseLayer and the associated file / directory ( WindowsContainersBaseImages ).

Picture 2 of What is the PortableBaseLayer partition in Windows 10 Disk Management?

GUID volume PortableBaseLayer and associated files / folders (WindowsContainersBaseImages)

Unexpected PortableBaseLayer will show up in the Disk Management or Optimize Drives list. And, in Windows Insider build 18912, some users have reported that the drive is not listed in Disk Management.

Is not! PortableBaseLayer has nothing to do with the Reserved Storage feature (also introduced in v1903).

Reserved Storage is a backup drive created to store Windows Update updates and temporary files, for a smooth installation experience. It has nothing to do with the Windows Sandbox or the PortableBaseLayer virtual drive.

Reserved Storage is automatically introduced on devices that come with 1903 pre-installed or on devices with a 'clean' 1903 installation.

Picture 3 of What is the PortableBaseLayer partition in Windows 10 Disk Management?

Reserved Storage is a backup drive created to store Windows Update updates and temporary files

You can learn more about Reserved Storage and how to disable it in the article: How to disable Reserved Storage on Windows 10.

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