First things first – you do this at your own risk. I take no responsibility for anything going wrong – and it can go wrong. If you are in doubt – don’t do it. And if it goes wrong – don’t blame me…

1. Make a DOS USB boot stick
   1. download the very useful Rufus from here.
   2. select “Create a bootable disk using FreeDos”:
      
   3. flash the USB.
2. Download the firwmare files from here: sas2008 (see footnote for original source)
3. Extract the files and place them on the root of the USB stick.
4. Download the latest LSI firmware from the Avago site. You’re looking for Firmware for an SAS 9211-8i Host Bus Adaptor. At the time of writing, this is version P20.
5. Extract the LSI firmware to a folder on your machine.
6. Create a subfolder on the USB called P20
7. From the extracted LSI firmware, copy the following to the P20 folder on the USB:
   1. The 2118it.bin file from <zip>\\firmware\\HBA_9211_8i_IT folder
   2. mptsas2.rom from sasbios_rel folder
   3. sas2flsh.exe from sas2flash_dos_rel folder
8. Look at the back of the card and note down the SAS address – it’s something like 500605B0xxxxxxxx.
9. put the card in the machine, and switch it on.
10. Boot to the USB stick – press F11 during POST and select USB.
11. Flash the firmware:
    1. Type the following:

       megarec -writesbr 0 sbrempty.bin
       megarec -cleanflash 0

    2. Reboot, again booting from the USB stick
    3. Next, install the P10 or P11 firmware – type the following:

       sas2flsh -o -f 2118it.bin -b mptsas2.rom
       sas2flsh -o -sasadd 500605bxxxxxxxxx (x= numbers for SAS address)
       

    4. Reboot, again booting from the USB stick
    5. Finally, upgrade to the P20 firmware – type the following to change to the folder and execute flash of the new firmware:

       cd p20
       sas2flsh -o -f 2118it.bin -b mptsas2.rom
       

12. Remove the USB stick
13. Reboot.
14. Some people recommend to disable loading the Option ROM. On my machine, loading the option room caused an NMI, so i ignored it, but if you want to do it: Load the Option ROM (press CTRL-C on boot) and set “Boot Support” to “Disabled”

The original instructions for this task are here, with my additions to update to the P20 firmware – I’ve archived them here for my own reference.