[CentOS] SSD drives for the OS - 1 or 2?

Tue Jan 5 00:26:29 UTC 2016
Rob Kampen <rkampen at kampensonline.com>

Preparing to build a small replacement server (initially built in 2005) 
and normally for the OS I would buy 2x500GB drives and deploy in a RAID 
1 configuration.
Now we have SSD drives available
- does just a single SSD drive offer the same reliability or is there 
advantage in deploying two in a Raid 1 config?

Also, what form factor / interface is best for the SSD OS boot device on 
a server M/B? Anything I should be looking for?
It seems most SSD are in laptop drive size, shape and interface - thus 
not a good fit into a server motherboard unless I'm missing something.
- what devices are you using?

Thanks in advance.