for raid you would need to buy a hardware raid card.
you could also by a cheap san/nas. synology is popular here.
for the usb esxi going bad, you could jsut backup your host config, and reinstall esxi if it does go bad.
here is howhttp://sparrowangelstechnology.blogspot.com/2012/08/esxi-how-to-backup-restore-host.html
Worst case if your USB fails you have to get another USB stick load ESXi up, configure networking then log in to it from your PC. Now just browse to the datastore and find the vmx files and right click, add to inventory. Your VMs are ready to go.
ESXi doesn't do software RAID. If you buy a RAID card you should get one on the compatibility list. Even on Windows RAID cards have always required very specific driver support as they still need to speak to the operating system in certain ways. Intel RS2WC080 is pretty easy to get a hold of and costs $350 AU. It only has two physical ports but the cables included go out to 8 drives. Supports 16 arrays and million drives if you daisy chain later to but who does that?
If its only a whitebox I'd consider running each drive as separate datastores and playing around with VSA or SvSAN and getting mirrored datastores happening.
Also consider plugging one of those drives into your PC and running one half of the mirrored appliance in it just in VMPlayer.
On 2nd thought with the money a RAID controller will cost you to get the best out of your lab I'd spend the same amount of money on a separate box and just run two HDDs on each box as separate datastores. A simple host with no HDDs you can get for about the same price as a RAID card. Make sure you
get something that will be compatible with ESXi. I have no idea about AMD stuff I have only used Intel. For example the Gigabye Z68AP-D3 works. Z68 and the Realtek on that model work. You do not need powerful processors in these boxes, I would recommend Intel G620s for whiteboxes for example. 16GB RAM per box and you will never have memory issues in a lab environment.
Learn what those apps I spoke about above do and you can test high availability and even fault tolerance without having to use nesting.
Thanks guys this has pretty much answered my questions for now.
As long as I can re-add the VMs from the datastore to a new ESXi host I have no reason to back up the host as it is just a basic build with no customization.
I will use 1 HDD to host the VMs, and another to host datastores for the VMs. I assume I can use the other 2 to backup the first 2. Is there a way to back up the VM and datastore in case the drive crashes so I can just reload the backup VM/datastore copy from the other drives? Does the clone option work for this? I just don't want to have a HDD go out and lose all my data and built OS VMs.
cehck out ghettoVCB
free backup, and you can sceduale it so that it will backup your vms to a different disk.
Thanks for the advice it seems this will do the trick.