What did you change before the reboot? Why the machine rebooted?
From what's on the screen there are 2 SATA controllers in the box, each with 2 drives plugged in. From your description, there should be 2 and 4 disks. Two disks have disappeared somewhere. Can you determine, why there are only 4 disks visible, instead of 6? Does re-plugging help? What does your raid controller say about the arrays?
Still, it's strange. If the boot disk disappeared, then where the kernel boot from? If the non-boot disks disappeared, why didn't the boot progress to the stage where a mount of some filesystem fails? If one disk from each group is gone, there shouldn't be any arror at the OS level at all... Something's very strange here.
Try re-booting again, but remove
quiet option from
grub command line, this should provide more information.