Windows 2025 unattended not installing Windows server to specified drive

Question

Below is the section of my unattend XML that is responsible for installing the Windows Server to a Disk/Partition. I was able to install Windows Server 2019 and 2022 with the same configuration. I would expect the install to be automated, but instead it performs no action at the first screenshot in my attachments. It is waiting for a user input and I believe it is because it is not able to install to Disk1 Partition2 drive, because when I manually try to install it to that I get the error message in the second screenshot "There is an error selecting this partition for install. Please select a different partition or refresh selection". It is not a very useful error message. After looking at similar issues online, I was able to manually delete the partition and install it to the newly created Disk tilted Unallocated Space. But this is not a good solution as it requires manual inputs where I need the installation to be completely automated.

<ImageInstall>

<OSImage> <InstallFrom> <MetaData wcm:action="add"> <Key>/IMAGE/NAME</Key><Value>Windows Server 2025 SERVERSTANDARD</Value> </MetaData> </InstallFrom>

<InstallTo> <DiskID>1</DiskID><PartitionID>2</PartitionID> </InstallTo> <WillShowUI>OnError</WillShowUI><InstallToAvailablePartition>false</InstallToAvailablePartition> </OSImage> </ImageInstall> <DiskConfiguration> <Disk wcm:action="add"> <CreatePartitions> <CreatePartition wcm:action="add"> <Order>1</Order><Size>450</Size><Extend>false</Extend><Type>Primary</Type> </CreatePartition>

<CreatePartition wcm:action="add"> <Order>2</Order><Extend>true</Extend><Type>Primary</Type> </CreatePartition> </CreatePartitions>

<ModifyPartitions> <ModifyPartition wcm:action="add"> <Format>NTFS</Format><Label>System</Label><Order>1</Order><PartitionID>1</PartitionID><TypeID>0x27</TypeID> </ModifyPartition>

<ModifyPartition wcm:action="add"> <Order>2</Order><PartitionID>2</PartitionID><Letter>C</Letter><Label>CORE</Label><Format>NTFS</Format> </ModifyPartition> </ModifyPartitions> <DiskID>1</DiskID><WillWipeDisk>true</WillWipeDisk> </Disk> </DiskConfiguration>


Answer 1

Hello,

Thank you for posting in Microsoft Community forum.

Based on the description, I understand your question is related to unattend.xml. 

Since there are no engineers dedicated to unattend.xml in this forum. In order to be able to get a quick and effective handling of your issue, I recommend that you repost your question in the Q&A forum, where there will be a dedicated engineer to give you a professional and effective reply.

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Thank you for your understanding and support.  If you have any question or concern, please feel free to let us know.

Best Regards,
Hania Lian

Answer 2

Check the logs C:\Windows\Panther\ in WinPE as well. If that's the case.

Windows Setup might be assigning letter C: to some other partition, causing that. It might be a 2025 behavior change, but we need MS to clarify.