4-disk RAID 6 drive fail now kernel panic

I have a 4 disk RAID 6 and one of the disks failed. I shut the system down to wait for a 4TB disc to arrive to copy all the data off. now when I boot it runs for about 20-30 seconds, the discs crunch and then i get a kernel panic. Is there a way to boot into a safe mode so that the discs do not mount automatically? This way I can mount read only or troubleshoot the discs? I would really like to be able to copy all this data and not lose it. any help is greatly appreciated.