I was encountering 'inaccessible boot device' after the first reboot when installing Windows 11 on a BIOS-configured RAID 1 array. It turns out that the RAID drivers I loaded at the start of the installation process were not copied over to the Windows drive. Here's how I used DISM after the first reboot to install the drivers and continue the installation:
1. **Boot into WinRE:** Use your Windows 11 installation media and select 'Repair your computer' to access the Command Prompt.
2. **Identify/Assign Windows Drive:**
* Type `diskpart`, then `list volume`.
* Find the volume corresponding to your Windows installation. If it lacks a drive letter:
* Select it using `select volume #` (replace # with the volume number).
* Assign a drive letter using `assign letter=D`.
* Type `exit` to leave diskpart.
3. **Inject RAID Drivers:** Use the DISM command:
* `DISM /Image

:\ /Add-Driver /Driver:E:\Drivers /Recurse`
* Replace `D:\` with your Windows drive and `E:\Drivers` with the path to the RAID driver folder.
* If the drivers are unsigned, add `/ForceUnsigned` to the end of the command.
* If you have a single .inf file, use `DISM /Image

:\ /Add-Driver /Driver:E:\Drivers\yourdriver.inf`
4. **Reboot:** Close the Command Prompt and restart. Your installation should proceed as normal.