I checked with one of our PERC performance gurus and this was his answer:

On the R900 with the 8 slot 2.5 bay, there is an A and B connector for the PERC6I. Connected to channels 0 and 1 on the PERC6I you would be able to run 4 on A and 4 on B. I’d recommend the A08 firmware for the card as it improves the RAID performance over A07.

Thanks,
Todd

Thanks Todd, that was what I thought. - Wolfgang.

Further to that... Can you actually build a RAID-Set acrosse the two channels 0 and 1.
What we might want to do is to create 1 x RAID1 (2 drives) and 1 x RAID 0+1 (2 x 3 drives).
Thanks, Wolfgang.

Again, I checked with one of our PERC performance experts -

The RAID adapter will see the 8 drives attached to it as a single set the same as the PERC6E. It will have them off port A&B, I've not tried to specifically span across channels before but since the drive ID's are unique there logically shouldn't be a reason you couldn't according to the MegaRAID settings.

Thanks,
Todd

Thanks for your quick answer. We'll give it a go then. Cheers, Wolfgang.