Disk read error after attempted Windows11 upgrade on z800 that had back door W11 install

[DavR0s]

Hi,

I have two "legacy" HP servers - a z600 and a z800 and recently tried to apply the latest Windows update:

2025-09 Cumulative Update for Windows 11 Version 24H2 for x64-based Systems (KB5065426) (26100.6584)

which worked fine on my z600.

I then tried it on the z800 and it seemed to go right through to very near the end of the process  ie the machine restarted and reported 100% install, and then when it restarted one final time I received a disc read error when loading windows to login to.

I recall that I need to use the same backdoor when upgrading the half year updates as the PCs arent compatible, but hadnt clocked it was there and assumed it would error on doing the update from compatibility issues.  But it seems to have attempted it and failed.

Given I cant boot windows is there any way of resolving this??

The disc seems fine as I can read it and see all the files when i put it in my z600.  If i get really stuck i think I have the Windows10 image so could potentially reinstall it and copy all my files across but that would be a long process so keen to avoid having to do that.

Thanks David

[DavR0s]

Just a little further information…..

….for some reason I am now getting a screen saying “Error:  Bios/legacy boot of uefi-only media” so it looks like the windows update has changed my boot files to uefi but my z800 doesn’t support that.

i tried to get the machine to enter repair mode (by turning off 4 times and holding the power button for more than 4seconds) but it just keep going to the UEFI error screen each time.

i have also found my windows10 disc that I originally upgraded to windows11 and this boots up fine.

so my options seem to be to somehow fix the UEFI message but I am not sure how to do this or if it’s possible, or repeat the w10 to w11 upgrade which is a bit more time consuming but I could encounter the same issue when applying the windows11 update.

Can someone offer me some advice who has more knowledge in this area, thanks

[DavR0s]

I gave up trying to fix my w11 setup.  So went back to the w10 image - tried to update it to w11 with exactly the same process ie the server upgrade to bypass compatibility issues that worked fine a few months ago (with the same files) and it errors out “Failed to launch the setup app”.  Anyone any idea why that would happen now?  In the meantime I’m back to using my w10 setup but that is clearly not a long term solution.

[SDH]

Your experience is an example of why I prefer the Rufus 4.9 method for upgrading to W11 24H2 on unsupported hardware. It provides a more "granular" control of the process. Rufus 4.6 (released to allow such upgrades to 24H2) has been updated now to 4.9, so that is the one to use.

If will be clean-installing of W11 24H2 on a HP workstation that DOES NOT support EFI/UEFI (such as the Z400/ Z600/ Z800) the creation settings of that Rufus 4.9 bootable installer thumb drive need to have the Partition scheme/Target system option bars set to "MBR" and "BIOS (or UEFI-CSM)", respectively, and your target boot drive needs to be partitioned as MBR rather than GPT... Rufus can do that for you during the W11 24H2 clean install from that thumb drive. You also should have your BIOS preset to factory defaults and be disconnected from the internet. When I hit Start the Rufus options page that opens gets all the boxes checked. You can fine tune BIOS settings later after the install. The install is quite streamlined this way, and after that is done I reconnect to the internet and do Microsoft Updates. I also have found the Intel Driver and Support Assistant utility to be worth installing.

A step I also do at the beginning of the clean install is to use DiskPart (the built in Microsoft OS utility) to clean and partition the target boot drive for a clean install (MBR partition the target boot drive if the workstation is not UEFI capable. GPT partition it if the workstation is UEFI capable). That seems to grease the skids for a smooth installation. See the attached DiskPart PDF below, and I explain how to launch an elevated CMD from inside the W11 installer in a separate post in this thread.

If you are going to do a clean install of W11 24H2 on a HP workstation which DOES support EFI/UEFI (such as the Z420/ Z620/ Z820 and up) the creation of a second separate Rufus 4.9 bootable installer thumb drive is necessary, with the Partition scheme/Target system options set differently... to "GPT" and "UEFI (non CSM)", respectively. Again, always pre-set the BIOS to factory defaults ahead of time, and make sure your BIOS is the latest version.

In either situation It is wise to work from the most recently released W11 24H2 .iso because Microsoft intermittently uploads those. This trick can save you from having to go through several unnecessary layers of W11 24H2 updating.

When you start out with a mishmash of OS components due to not having a proper clean install to build from you can suffer the error messages that indicate mixing of MBR and GPT/ BIOS and UEFI OS components, as you have just experienced. That risk is significantly higher if you do an "in-place" update rather than a clean install. I have not seen such error messages since properly understanding and using these clean install methods.  Yes, it can be a PITA, but it is worth doing things correctly.

A quick 12-minute related video: https://youtu.be/75Hg866SJI0

[SDH]

An added tip worth knowing is that Microsoft has provided a way to launch an elevated CMD prompt from inside an open Windows 11 installer, and a Rufus 4.9 modified W11 24H2 installer on the thumb drive also carries that feature. When you boot from a Rufus W11 installer thumb drive you simply hit the key combo of Shift + F10. From inside that elevated CMD prompt you then launch DiskPart. For your non-UEFI Z600's clean install you'd include use the command "convert MBR" instead of "convert GPT" after you had selected the correct target drive and cleaned it. You exit out of DiskPart by entering the command of "exit" and then "exit" again to close the elevated CMD prompt. Then you can proceed with your clean install. Handy.

As always it is important to pay close attention to what you're doing when you clean a drive... DiskPart shows the sizes of the target drive and your thumb drive to help you pick the correct one. I always make sure I don't have any other drives in place at this stage to prevent mistakes. They can be added back in later.

[DGroves]

the z800 can run windows 11 as SDH pointed out however the "feature updates" will not auto install from windows update when using a win 11 install that has the CPU/TPM check bypassed (which the z800 requires) it also requires that the install be done using the LEGACY/MBR configurations normal security and .net updates will however auto update

I agree with SDH that using rufus to create a usb based win 11 install key is the way to go

the feature updates can be manually installed once MS has released them simply google for a method you like and follow the directions 

 3TB and larger can't be used as a bootable drive

data (non boot) drives can be any size and must be in GPT format if over the 2.8GB limit 

attached is a later (latest?) HP z800 quickspecs

[SDH]

All good points by DGroves, and he has helped me figure out many of these upgrade methods. The next big feature upgrade from Microsoft will be released shortly, likely within the next 4 weeks, as W11 25H2. The code for that is supposedly already largely inside your W11 24H2 build and the code will be unlocked by a planned activation process. We will see if that is as easy as it sounds for those of us running W11 24H2 on unsupported hardware.

Personally, I don't think Microsoft really wants to create a massive pile of eWaste, and this approach is working very well for many happy customers as is.

[DGroves]

people using the modified/hacked windows 11 24H2 installers

that bypass the CPU/TPM hardware checks during the OS install

will be ineligible for the MS auto update through the microsoft update servers

and will either need to do a clean OS install of a modified 25H2

or perform a hacked/modified inplace 24H2 to 25H2 upgrade

[DavR0s]

Hi, thanks for all the advice and suggestions.  I have tried the Rufus approach as suggested (using v4.9) and the good news is I am getting further in the process.  It does the windows update, asks me to agree and allows me to keep my current settings and data, but the I get an error “an unsupported operation was attempted”.  If I search on this it says that it may be because the machine is incompatible (but it has run W11 recently for a couple of months so I know it’s capable.  It also says to extend the registry to by pass the hardware checks but I still get the error.  The next suggestion was to go to Rufus 3.22 or earlier and going back a version of w11 as there is suggestions that the latest w11 has further checks??

i though I’d check in for any suggestions as to what to do?

btw on an unrelated question if I do a clean w11 install will it use my existing key,  I am primarily upgrading and not doing a fresh install to preserve the key

[DavR0s]

I have progressed things since the last post.  I discovered someone else has experienced the same issue and the solution is not to include the updates when upgrading to W11.  So I have now passed the point where the problem was occurring and it’s finishing off the final install stages now.

The question now is will it allow updates to then be applied - particularly as it was a recent update from W11 on this machine that failed and rendered my machine unusable.

Will let you know how I get on!

David