Windows 10 version 1903 will automatically reserve around 7 GB of device’s disk space to store updates and optional files to prevent Windows Update failed due to insufficient storage, starting from May 2019 Update. You can recover Reserved Storage with following steps.
Windows 10 Reserved Storage
Content Summary
Check whether Reserved Storage enable
How to Disable Reserved Storage
Check whether Reserved Storage enable
Step 1: Go to Settings > System > Storage.
Step 2: Click Show More Categories.
Windows 10 Storage Show more categories
Step 3: Click System & Reserved.
Windows 10 System and Reserved
Step 4: You will see Reserved Storage section with 7+ GB of storage space in use if Reserved Storage is enabled.
Windows 10 Reserved Storage enable
How to Disable Reserved Storage
Step 1: Go to Start and typing regedit to open Registry Editor.
Windows 10 Registry Editor
Step 2: Navigate to the following key:
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\ReserveManager
Step 3: Double-click ShippedWithReserves
entry.
Windows 10 ShippedWithReserves registry key
Step 4: Change Value Data from 1 to 0 then click OK.
Windows 10 ShippedWithReserves registry key value data
Step 5: Close Registry Editor and reboot Windows 10 to apply the changes. You may have to wait few weeks before Windows installs an update and deletes the reserved storage.