[Gluster-users] to RAID or not?

[Gandalf Corvotempesta]

Let's assume a small cluster made by 3 servers, 12 disks/bricks each.
This cluster would be expanded to a maximum of 15 servers in near future.

What do you suggest, a JBOD or a RAID? Which RAID level?

15 servers with 12 disks/bricks in JBOD are 180 bricks. Is this an
acceptable value?
Multiple raid6 for each servers? In example, RAID-6 with 6 disks and
another RAID-6 with the other 6 disks. I'll loose 4 disks on each
servers, performance would be affected and rebuild times would be huge
(by using 2TB/4TB disks)

Any suggestions?