blackduck30

Ok in a nut shell you should be able to add your hard drive to your existing raid array via the intel matrix utility, I know it can be done with a single drive into a raid by adding an additional drive, but I am not sure if it will work with an existing arrary. From memory you have to have admin privileges or be logged in as the admin and then open up the Intel matrix utility, on the top of the utility there should be an "action" tab and from inside that there should be an option to migrate another drive.
I will have a look through and see if i still have my manual for it , I have gone to nvidia raid now but i am a horder of manuals so just have to find it.

The only way i see around it if it does not let you migrate another drive in is to clone your existing array over to your new drive using XXclone and make sure you make it bootable. You can then confirm you can boot to the cloned drive by changing the boot order in your bios to boot to it. If this goes well and you can boot into it without problem you should by rights be able to delete the old array and then go backinto the intel utility and migrate the other 2 drives into a raid 0 as your single drive should be raid ready.

Steps on Setting Up a “RAID Ready” System

In order to set up a “RAID Ready” system, complete the following steps:
The system must meet all the “RAID Ready” system requirements specified in Section 18.2.

1. Intel Application Accelerator driver is installed during operating system installation; you will be prompted to ‘Press F6 if you need to install a third party SCSI or RAID driver’ or preinstalled on a SATA Hard Drive (configured as Non-RAID Disk – also known as RAID Ready Mode)

2. Intel Application Accelerator driver is installed from within operating system to add Start Menu links and the Intel Storage Utility Converting a “RAID Ready” System into RAID 0 or RAID 1 System with Migration Feature
Note: The steps listed in this section assume that the operating system has been installed on an existing Serial ATA hard drive and the required driver was installed during the operating system setup.

To turn a RAID Ready system into a RAID System, complete the following steps:
1. Physically add one Serial ATA hard drive in the system
2. Boot to Windows*, install the Intel Application Accelerator
3. Open the Intel Storage Utility (Start/All Programs/Intel Application Accelerator/Intel Application Accelerator) User's Manual 63 “RAID Ready”
4. Create a RAID 0 or RAID 1 volume via the Intel Storage Utility and perform a ‘Create from Existing Disk’ migration (right-mouse click on ‘RAID Volumes’ or select option under ‘RAID’ file menu)
5. When migration is complete, Reboot
6. Optional: Use 3rd party application or Windows* to create and format a new data partition on
unused space, if any (see Note below)

Note: To ensure that non-Windows* partitions are kept intact, the migration to RAID 0 or RAID 1 does not utilize the extra space made available by adding the second hard drive. To take advantage of the extra hard drive space you will need to do one of the following:

1. Create a new partition using Windows Disk Management (See Section 18.4.1 for instructions)
or
5. Extend the partition to fill the rest of the available space. Windows does not natively include
tools to do this, but there are 3rd party software utilities to accomplish this such as
PartitionMagic* or Partition Commander*.


All I can say is if you are not confident with playing with an array or not comfortable trying something out of the norm I would stay with a 2 drive array or just start from scratch with a reinstall.
If you do try anything PLEASE backup everything you can not afford to loose or replace as i can not guarantee any sucess but in theory it should work