To have a bootable raid 0 you can’t use iRST.
First you need to enable raid in the bios. This should be in your manual. Please not that turning on raid usually turns it on for several sata ports. Make sure the drives you want to have in the raid are on one of those. Often the last two ports are left as AHCI which is perfect for using for your optical or single HDD’s. Save and exit the bios.
Next, you setup the drives in the raid bios (Ctrl+i during when prompted) You will need to add the drives to the array and then format the array, so plan on this taking some time. Also if there is anything on either of the drives that needs saving then please back them up first.
Once you get the array setup, now you can boot from your install media and load windows to it. Win10 should recognize the array right from the start whereas win7 will need you to load the raid driver during the part where it asks if there are drivers you need to install
Alright, now you have windows loaded and can boot from it. Being Raid0, if either drive fails then the array is lost with all data on both drives (data is stored across both drive in a 4bits on this one, 4 on that one) so you cannot recover from only half the data. I typically install all my motherboards drivers, windows updates, and base software (which is stuff I always install like Antivirus) and then I take an image of this basic installation. An image can be restored very fast and save you a few hours work. I use Macrium Reflect which the free version also works very well. If you use something else please make sure it can restore to a raid, several cannot. Then create an image regularly and you can get back to this point anytime something goes wrong like a windows update gone awry. I try to make sure I have one before I let windows update
Have a great day and remember that the only way to protect your data is to have backed it up to multiple external media. I make more and keep 1 copy offsite. I like to plan for the house burning to the ground…