To answer my own question: It seems that it is possible to use both HDD in recovery mode but I needed to create the RAID Recovery Array through the Intel ROM, not Intel RST in Win7. The negative side effect is that all data on both disks will be lost! So I restored my Acronis image to the new array. Unfortunately Intel RST in Win7 did not manage to mirror the master disk to the external eSATA drive correctly hereafter. I had set the array to manual recovery update mode. As soon as I started manual update it took a couple of seconds and told me that it has finished mirroring which is not possible in that short time. So I had to go back to the Intel ROM, reset the recovery disk and then rebuild the recovery disk in Win7. This took a very long time as expected. BTW: If you need to check for errors it seems that you need to switch to immediate update mode first and then start checking. In manual update mode this option is not available. In conclusion, the whole rapid recovery thing is nothing I would really rely on. There are some instabilities and strange things going on. It is also possible to receive some blue screens.
