O Raid 6 é caro, mas é mais seguro. Não tenho certeza se você tem a opção de criar raid 6 + 0 que na minha opinião é melhor porque tem mais performance (por causa da tarja) ... enfim, qualquer raid usando + 0 tem a metade da capacidade ... então balanceia entre suas necessidades:
Raid 5 -> Cheaper, it protects against 1 broken hdd. You lose only 1 hdd of capacity.
Raid 6 -> Expensive, it protects against 2 broken hdd. You lose 2 hdds of capacity.
Raid 1 -> Mirror. You sacrifice the half of capacity to have more secure raid. You can lose the half of hdds.
Raid 0 -> Stripe. If you lose any disk, you lose all your raid, not recommendable for production environments. Only recommended if combined (5+0, 6+0, or 1+0).
Raid 5+0 -> The combination of raid 5 and raid 0. You sacrifice the half + 1 hdd of capacity to have more performance and it can avoid one hdd broken on each subarray.
Raid 6+0 -> The combination of raid 6 and raid 0. You sacrifice the half + 2 hdd of capacity to have more performance and it can avoid two hdd broken.
Raid 1+0 -> The combination of raid 1 and raid 0. You sacrifice the half of capacity to have more performance and it can avoid one hdd broken on each subarray.
Aqui está uma tabela para comparação:
Umlinkcomalgumasdescriçõessobreinvasões.