RAID5 is similar to RAID6, but with two parity stripes. I.E., two drives can fail.
Plus, with modern drives, what's the true failure rate? It's pretty darn low.
thlnk3r: LOL... if he wants 4-5TB, with SAS indeed you'll need an unlimited budget
I think the largest SAS drive is in the ~300GB range, and hundreds of dollars for a single drive.
Have you thought about RAID10 or RAID0+1? In those cases, you can use the onboard controller (performance will be as good as RAID50 or RAID6 on a dedicated true hardware controller). You'll need eight (8) 1TB drives to get 4TB of storage space. With, for example, these Seagates
, that'll cost you $1,679.92
The alternative is RAID50 with six of those drives on a dedicated controller. Six of the same Seagates will ring you up $1,259.94 and a decent controller card that supports RAID50
will cost you $449.99. Total cost: $1,709.93. Basically a tie, but RAID10 or RAID0+1 is much easier to rebuild in case of failure.
Personally, I do NOT recommend RAID for ANY important data... I'd highly consider a SINGLE external drive for your most critical data (or a tape device...). Then schedule nightly backups to that drive. The issue with RAID is that the moment you replace the RAID controller with another type, you'll have to rebuild the RAID array. Imagine that in a year or two your RAID controller bites the dust, and it's impossible to get a replacement. Ok, worst case scenario, but still.