I had ubuntu installed with raid 0 enabled. I have added 2 more disks went into the bios deleted and created a new raid setup using raid 10 (total of 4 disks now).
However during install of ubuntu server it asks if it should activate the RAID Sata disks, I tell it yes. Next step shows up blank for available disks when determining where to mount the root etc. Anyone have a clue as to why this would be?
My guess is that you have a fakeraid ( see http://wiki.ubuntu.com/FakeRaidHowto for background info ). Fakeraid is not supported as well as conventional software raid, so you should not use it if you don't need to dual boot with Windows. Go into the bios and delete all traces of the raid array, and when you run the Ubuntu server installer, just set up a conventional mdadm software raid.
Before you do that though, if you could file a bug report on launchpad.net against the dmraid package in ubuntu, and attach to that report the files generated by running sudo dmraid -rD, I would appreciate it. This way I may get around to fixing the problem. You can do this from the livecd.
I've noticed Disk Utility recognizes my dm-raid drives twice. For example, my RAID0 drive (two 200GB drives) shows up as dm-0 (400GB) and dm-4 (400GB). Perhaps you need to activate a different one.
One thing that sounds odd there is that term "activate". I'm not sure that the installer should need to activate a dm-raid partition (what you're trying to use); I've only noticed that with Linux-based softRAID.
Also, you might need to reboot & restart the installer. I've seen it fail many times when saving changes to partitions; after a reboot, the changes are intact and the installer recognizes them.