How to Enable Reserved Storage Using DISM or PowerShell in Windows 10 Version 2004
Reserved Storage first shipped in the Windows 10 May 2019 Update (version 1903). When enabled, it keeps some disk space for Windows Update, apps, temporary files, and system caches because without enough disk space, Windows and applications stop working properly. Updates may also fail to install if there isn’t enough free disk space.
Users installing a fresh copy of Windows 10 1903 or later, or receiving a device with the OS preinstalled, should see Reserved Storage enabled out-of-the-box. Some device manufacturers choose not to enable Reserved Storage because it reduces the available disk space to users.
Those upgrading from a previous version of Windows don’t get Reserved Storage, unless the ShippedWithReserves registry key is set to 1 before the upgrade. You can find the key under HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\ReserveManager.
Windows Update and Reserved Storage
Windows Update gets priority access to Reserved Storage. Before an update, temporary files that are no longer needed in Reserved Storage are deleted. The remaining space is then given exclusively to Windows Update. If Reserved Storage still doesn’t have enough space, Windows Update can also spill into free disk space that is available to the user. On systems where disk space is severely limited, Windows Update might also prompt to attach external storage, like a USB drive, to complete the update process.
For more information on Reserved Storage, see What is Windows 10 Reserved Storage on Petri.
DISM updated with new Reserved Storage options
Microsoft announced at the beginning of April that an update to the Deployment Image Servicing and Management (DISM) tool in Windows 10 version 2004, which is due to drop soon, will include new options for managing Reserved Storage. The new version of DISM will let administrators enable Reserved Storage on machines that were not shipped with Windows 10 1903 or later but that have since been upgraded to version 2004 or later.
Admins will also be able to query the amount of space reserved and disable Reserved Storage. The state of Reserved Storage is preserved across OS upgrades once it has been enabled or disabled using DISM. The following DISM command enables Reserved Storage for the online Windows image:
DISM /Online /Set-ReservedStorageState /State:Enabled
Changing the /State parameter to Disabled turns off Reserved Storage. Running DISM /Online /Get-ReservedStorageState shows whether the online Windows image has Reserved Storage enabled.
Enable or disable Reserved Storage using PowerShell
If you don’t want to mess around with DISM, Windows 10 version 2004 supports a new PowerShell cmdlet that will let you enable or disable Reserved Storage for online images.
Set-WindowsReservedStorageState -State Enabled
Similarly, to disable Reserved Storage, use the command above but change the value of -State to Disabled. Running Get-WindowsReservedStorageState shows you the current state of Reserved Storage with the online Windows image.
Microsoft says that these new capabilities are available via DISM, PowerShell, and the DISM API. If you have a Windows management tool that is not aware of Reserved Storage, i.e. usually those that don’t use Windows Update, Reserved Storage should be disabled prior to applying an update. Once an update is complete, Reserved Storage can be re-enabled.