HP Z800 killed with KB5066835 that cause boot failure, "A Disk Read Error Occurred" if you uninstall

[akierum]

HP Z800 killed with KB5066835 that cause boot failure, "A Disk Read Error Occurred" if you uninstall it error still there, any way to solve?

[akierum · Accepted solution]

Easy FIX you must restore the 100MB partition with windows boot files using Terabyte Unlimited etc, software that you made before the KB5066835 update. After restored the PC boots normal again. There is no other fix.

[vanadu]

I would like to know how you can use the Windows software you mentioned to restore the 100MB partition if you can't start Windows? Can you please be more specific with your answer? 

Thank you!

[SDH]

I also would appreciate more details from Akierum. I'm wondering if he was trying to drum up business for that company he mentions.

There is a lot of google info available on the "A disk read error occurred" message. I've personally seen that after a successful W11 24H2 install on a Z600, only to be borked by a subsequent W11 24H2 update producing that error message against a black background. A hopeful video is here:

https://youtu.be/G2STQCEitvA

That is based on a Dell computer... and has glowing kudos in the comments section. That same BIOS option is available on some but not all HP workstations. Unfortunately, not on the Z400/ Z600/ Z800 workstations. Here's the deal:

HP has had variable wording and settings in BIOS for the SATA emulation mode in their workstations. In the ZX00 BIOS it is "RAID + AHCI" or "IDE", with no separate option for just "AHCI". In other workstations it has been "RAID" (meaning RAID + AHCI), AHCI, or IDE. Also, RAID + AHCI, AHCI, or IDE. Why the mishmash I have no idea.

For all more recent HP workstations you would be able to try the AHCI-alone BIOS trick.

Another approach is to use a same-version Rufus or Microsoft OS installer thumb drive, boot from it, and on the opening page choose the repair option. You can get into the recovery environment that way and google will find you the numerous commands you can try to recovery your boot volume, targeting your boot SSD. Some say the volume should be more than 100MB... and recommend 300MB instead. However, that needs to be done before the OS install, and can be done via use of DiskPart from within the booted USB drive. Never fun, and it is hard to blame Microsoft for issues we might uncover experimenting with old hardware and new W11 releases.

[vanadu]

Thanks for this SDH. I agree that this Akierum user does not seem legit, especially since the company he's hawking wares from doesn't appear have a product you can load onto a USB or WinPE.

I think it's time to start a new thread for this W11 issue since it's bound to come up again with W11 updates and Zx00 machines. I'm not sure this Zx00 issue is related to the one in the video. I was able to do the in-place upgrade on my dual-boot Z600 with no problems at all -- even the dual boot to Ubuntu with Grub worked perfectly for three days and at least 10 reboots. Then, after the latest update, 'A disk read error' when booting to W11. Grub to Ubuntu still worked fine. So whatever they did, it happened in the update between 11/7 and 11/10. 

I need to work this out -- not ready to brick this Z600 box yet with all the mods and programs I've done over the past few years. @SDH, you and Paul are the senior gurus here, maybe you'd like to start a new thread? I don't want to give the OP's software plug any more face time here than absolutely necessary, and I think a more descriptive post title would be in order. In fact, unless the OP shows face here again, maybe this post should be put in the Spam folder (i.e. deleted). My $0.02...

[akierum]

You guys think I work in a fire department or something, you do not pay me, and I owe you nothing.

I shared that on my Z800 PC the easy fix is to take a backup of whole SSD disk using the Terabyte Unlimited that easily allows to back up and restore whole drive and separate partitions. 

You can use Acronis or whatever Linux sudo freeware crap you want, I just use what I have found works best.

The Z800 or Z600 does not have the non RAID version of HDD control (In the ZX00 BIOS it is "RAID + AHCI" or "IDE", with no separate option for just "AHCI") so this is the only way.

[SDH]

Edit... apologies to Akierum.  Any help you can provide will be greatly appreciated.

Vanadu, agree on value of a post dedicated to and titled for the bigger picture re ZX00 workstations. There are a lot still doing good work. You may wish to start a thread and I'll contribute. Paul's favored approach is different from the Rufus approach. It would be interesting to hear from him on Windows updates bricking builds. So far, my new clean Rufus 25H2 is holding up through updates. And, don't forget the DGroves factor. He knows things very few of us do, and surely has some good ideas on the issue.

[vanadu]

My apologies to Akierum, too. I thought you were a 'hit and run' guy trying to sell product. 

If I'm understanding this right, the solution only works if you have a backup of the W11 build before the KB5066835 update. I guess I was looking for a way to get past the 'disk read error' without restoring from an existing backup.

Again, sorry for overreacting. My mistake.

Vanadu

[vanadu]

OK, I'll post a new thread as soon as I can get my SDD restored from the stone-age HDD where I have the pre-upgrade W10 backup saved. Thanks - and again my apologies to the OP for hijacking his thread.

[akierum]

@Vanadu

"If I'm understanding this right, the solution only works if you have a backup of the W11 build before the KB5066835 update. I guess I was looking for a way to get past the 'disk read error' without restoring from an existing backup."

Yes you must have a backup that's a guaranteed way for a fix, else 

ChatGPT suggests this:

Got it — since your Z800 is running in RAID mode, that explains a lot.
After KB5066835, Windows is breaking the Intel Matrix Storage / RST (ICH10R) driver chain used by the Z800’s onboard RAID, which leads to “A Disk Read Error Occurred” long before bootrec can fix it — because the bootloader literally can’t read the array correctly anymore.

Let’s go through what’s actually happening and what can bring it back.

---

🧠 Root Cause (confirmed on Z800s & Z600s)

• KB5066835 replaces storport.sys, iaStorV.sys, and sometimes bootmgr.

• On legacy BIOS + Intel RAID (ICH10R) setups, the new drivers no longer correctly enumerate the RAID volume at boot.

• That triggers the “A Disk Read Error Occurred” message from the BIOS level — not from Windows itself.

• Uninstalling the update in Windows (from another system) won’t help because:

  • Boot files on the System Reserved partition are still mismatched.

  • iaStorV.sys (the Intel RAID driver used at boot) stays broken.

---

🧰 What you can do (tested on Z800/Z600)

Option 1 — Restore old storage driver manually

If you can access the drive using another PC or via WinPE:

1. Boot from Windows 10 installation USB → Shift + F10.

2. Mount your system drive (e.g. C: or another letter).

3. Rename the broken RAID driver:

   cd C:\Windows\System32\drivers ren iaStorV.sys iaStorV.bad

4. Copy back the pre-update version of iaStorV.sys.
   You can get it from:

   • C:\Windows\System32\DriverStore\FileRepository\iastorv.inf_amd64_…

   • Or another working Z800 (same Windows build before KB5066835).

   Example:

   copy D:\iastorv.inf_amd64_*\iaStorV.sys C:\Windows\System32\drivers\

5. Also check storport.sys and bootmgr if their timestamps changed around the update date.
   If needed, copy them from C:\Windows\WinSxS\... or from another machine with the same build pre-update.

6. Then rebuild BCD again:

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

7. Reboot — it should detect the RAID volume again.