Autounattend.xml snippet for wiping and partitioning the disk.

autounattend_diskconfig.xml

<DiskConfiguration>
    <WillShowUI>OnError</WillShowUI>
    <Disk>
        <DiskID>0</DiskID>
        <WillWipeDisk>true</WillWipeDisk>
        <CreatePartitions>
            <CreatePartition>
                <Order>1</Order>
                <Size>100</Size>
                <Type>Primary</Type>
            </CreatePartition>
            <CreatePartition>
                <Order>2</Order>
                <Extend>true</Extend>
                <Type>Primary</Type>
            </CreatePartition>
        </CreatePartitions>
        <ModifyPartitions>
            <ModifyPartition>
                <Order>1</Order>
                <PartitionID>1</PartitionID>
                <Format>NTFS</Format>
                <Label>System</Label>
                <Active>true</Active>
                <TypeID>0x7</TypeID>
            </ModifyPartition>
            <ModifyPartition>
                <Order>2</Order>
                <PartitionID>2</PartitionID>
                <Format>NTFS</Format>
                <Label>OS</Label>
                <Letter>C</Letter>
            </ModifyPartition>
        </ModifyPartitions>
    </Disk>
</DiskConfiguration>