How To Resize / Recreate MBR System Reserved Partition

Windows upgrades may fail if the System Reserved partition is too small. This guide explains how to resize or recreate it to ensure smooth updates.

Follow these steps carefully to avoid common installation errors.

Background

During installation, Windows automatically creates a System Reserved partition. This partition contains the Boot Manager, Boot Configuration Data (BCD), startup files required before the C drive is mounted, and BitLocker metadata (if enabled). If the partition is undersized, upgrades may fail with errors such as 0x800f0922 because boot files cannot be updated.

Important Notes Before You Begin

• Backup: Always back up your data before making partition changes.
• Layout: This procedure applies to Legacy BIOS/MBR systems, not GPT.
• Tools: You will need a third-party partition manager (MiniTool, EaseUS, GParted).
• Media: Windows installation USB is required.

Step 1: Prepare Space with a Partition Manager

Using MiniTool Partition Wizard as an example:

1. Download and install MiniTool Partition Wizard.
2. Shrink the C partition by about 450 MB from the left side:
   • Right-click C, choose Resize/Move, then drag the left boundary to the right.
   • This creates unallocated space directly before C.
3. If unallocated space appears to the right of C, expand C as needed.
4. Expand System Reserved into the new space:
   • Right-click System Reserved, choose Extend, then select the unallocated space.
   • Ensure it remains NTFS and Active.
5. Apply changes and reboot.

Step 2: Boot into Windows Setup

If extending isn’t possible, recreate the partition:

1. Insert the Windows 10 installation USB.
2. Boot into BIOS and set boot order to USB.
3. At the Windows Setup screen, press Shift + F10 to open Command Prompt.

Step 3: Recreate System Reserved Partition with Diskpart

diskpart
list disk
select disk 0
list partition
select partition 1
delete partition override
create partition primary size=500
format fs=ntfs quick label="System"
active
assign letter=v
list volume
exit

This deletes the old System Reserved partition and creates a new 500 MB NTFS partition, marked Active.

NOTE: Replace 0 with your Windows disk number.

Replace 1 with your System Reserved partition number, if needed.

NOTE: Record your Windows volume and System Reserved volume letters from the 'list volume' command.

Step 4: Rebuild Boot Files

bcdboot C:\Windows /s v: /f BIOS

Replace C: with your Windows partition letter if different, and v: with your System Reserved partition letter.

Final Step

Exit and reboot. Your system should now boot with the new System Reserved partition.

By resizing or recreating the System Reserved partition, you ensure compatibility with Windows upgrades and maintain a stable boot environment.

This process future-proofs your system and prevents upgrade errors related to insufficient partition size.