Windows 2012 Autounattend still asking about disk configuration

Solution 1:

On MDMarra's suggestion in Chat, I added a system partition to the manifest.. Something required for EFI compatibility, apparently.

This, now, seems to work.

So it looks like Windows 7 has no specific requirement to have a System Partition (although it will be created automatically in a non-unattended installation), whereas Windows Server 2012 will fail to install without a system partition.

Creating the partition is as simple as putting 0x27 in the TypeID box for the partition.

<DiskConfiguration>
                <Disk wcm:action="add">
                    <CreatePartitions>
                        <CreatePartition wcm:action="add">
                            <Order>2</Order>
                            <Type>Primary</Type>
                            <Size>71800</Size>
                        </CreatePartition>
                        <CreatePartition wcm:action="add">
                            <Order>1</Order>
                            <Size>512</Size>
                            <Type>Primary</Type>
                        </CreatePartition>
                    </CreatePartitions>
                    <ModifyPartitions>
                        <ModifyPartition wcm:action="add">
                            <Active>true</Active>
                            <Format>NTFS</Format>
                            <Order>2</Order>
                            <PartitionID>2</PartitionID>
                        </ModifyPartition>
                        <ModifyPartition wcm:action="add">
                            <TypeID>0x27</TypeID>
                            <PartitionID>1</PartitionID>
                            <Order>1</Order>
                            <Active>false</Active>
                            <Extend>false</Extend>
                            <Format>NTFS</Format>
                        </ModifyPartition>
                    </ModifyPartitions>
                    <DiskID>0</DiskID>
                    <WillWipeDisk>true</WillWipeDisk>
                </Disk>
                <WillShowUI>OnError</WillShowUI>
            </DiskConfiguration>