How I Fixed 100% Disk Usage on My Windows 11 Laptop
Are you struggling with a laptop that suddenly becomes unresponsive or extremely slow? On my Fujitsu LIFEBOOK U Series (Windows 11 Pro), the keyboard was lagging, and sometimes the whole system froze. After checking Task Manager, I noticed that the disk usage was constantly at 90–100%.
This article is for anyone facing similar issues — especially those using older laptops with SATA SSDs or HDDs. Let’s walk through what didn’t work, what finally did, and how you can try it too.
Fixes That Did Not Work
1. Disabling Windows Search
Windows Search can cause high I/O activity. I stopped the service via services.msc → right-click Windows Search → Stop, but it had no effect.
2. Disabling SysMain (Superfetch)
While SysMain preloads apps into memory, it’s known to cause disk issues on SSDs. I disabled it via the same method but saw no improvement.
3. Running chkdsk
I ran chkdsk /f /r to check disk health, but it showed no errors. The problem persisted.
4. Searching for Official Fujitsu Drivers
I checked Fujitsu’s official support site but found no known issues regarding “100% disk usage” for LIFEBOOK models.
5. Real Cause: MSI Mode for AHCI Controller
Some users on Microsoft forums and Dell support mentioned that AHCI with MSI mode enabled can cause SSD I/O problems resulting in high disk usage. So I tried disabling MSI.
Why does this help? MSI (Message Signaled Interrupts) is a way for Windows to handle communication with hardware devices. However, in some systems with certain AHCI drivers, enabling MSI causes abnormal disk usage. Disabling it forces the system to use legacy interrupt handling, which may resolve the issue.
How to Fix It (Step-by-Step)
⚠ Warning: This method involves editing the registry. Please proceed at your own risk and back up your system first.
We strongly recommend that you back up your registry or create a restore point before making any changes. Although this method is known to work on many systems, editing the registry always carries some risk.
Step 1: Get Device Instance Path
① Open Device Manager
② Go to IDE ATA/ATAPI Controllers → right-click Standard SATA AHCI Controller →Properties
③ In the Details tab, choose Device Instance Path from the dropdown
④ Copy the full string — you’ll use it in the Registry Editor
Step 2: Edit Registry to Disable MSI Mode
① Open Registry Editor by typing regedit
② Navigate to:HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Enum\PCI\\(your device path)\\Device Parameters\\Interrupt Management\\MessageSignaledInterruptProperties
③ Double-click MSISupported and change its value from 1 to 0
④ Close the Registry Editor and restart your PC
What Happened After Reboot?
After the reboot, the disk usage dropped dramatically within seconds.
No more lag, freezes, or input delays. This simple registry tweak worked like magic.
Final Thoughts: Should You Try This?
Who should try this? This fix is most effective for users running older laptops or desktops with SATA-based SSDs or HDDs — especially those who upgraded to Windows 10 or 11 and started experiencing high disk usage.
This method won’t fix every case of high disk usage, but it’s worth a try if you’re using an older laptop with AHCI and SSD. It could be the breakthrough you’ve been looking for.
Tip: This fix also applies to some Dell and Lenovo machines. Always confirm your controller type before making changes.
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💡 Looking for more tips? Check out our full list of Windows Help Guides.
