I've been doing some research on Micron 1100 2TB ssd's and they seem to offer a lot of value for the money.  I'm considering using smaller cheaper SSDs for boot drives and using one 2TB micron SSD in each host for a glusterFS replica 3 setup (on the fence about using an arbiter, I like the extra redundancy replicate 3 will give me).

My question is, would I see a performance hit using only one drive in each host with glusterFS or should I try to add more physical disks.  Such as 6 1TB drives instead of 3 2TB drives? 

Also one other question.  I've read that gluster can only be done in groups of three.  Meaning you need 3, 6, or 9 hosts.  Is this true?  If I had an operational replicate 3 glusterFS setup and wanted to add more capacity I would have to add 3 more hosts, or is it possible for me to add a 4th host in to the mix for extra processing power down the road?

Thanks!