Custom NAS questions (mostly RAID)


I've seen some other people posting about their NAS builds but I still had a few questions. I'm going to be building my own with FreeNAS.

Here's the basics of what I'm leaning toward:

- 3 x 3TB drives

- I've seen the rule of thumb about 1GB RAM per 1TB (I assume 8 GB would be plenty of RAM for 3x3TB)

- Some sort of low-end dual core processor (open to suggestions)

- This will only be accessed over LAN by no more than 4 users.

- This is a media server that I want to be optimized for streaming HD videos via XBMC or PLEX.


My biggest question is about RAID. My roommate has a non-custom Netgear NAS that uses their proprietary x-raid2, which I won't be able to use since I'm building custom. I won't have access to his NAS in a few months, which is why I am building my own. I've seen a few places that say to go with RAID 5. I wanted to see if anybody here had suggestions based on what they use. I want to be able to use at least 6TB out of the 9 that will be in there, with a high read speed.



You are partially right in your facts. The 1GB of RAM per TB of storage is for when the drives use ZFS, as it aids with calculations. In which case you would require a decently paced CPU. Fast Dual at least.

If you are planning on using a RAID card, then the system itself doesn't need to be anything special as the RAID card will be doing the majority of work (disk access and calculations for data striping). RAID cards can also be pretty expensive (unless you prowl ebay for something like a DELL Perc6).

The alternative would be to use a ZFS RAID (RAIDz) similar to raid 5 but doesn't require a dedicated card. However it does require the beefier hardware to do the checksum calculations as the drive reads and writes; and unlike RAID 5 where you can theoretically get n -1 disk speed (so a 3 disk array reads at the speed of 2) RAIDz reads at a max of equivilant to one drive (so the 3 disk array would read at 1 disk speed)

The speed issue with RAIDz isn't too big a deal when only using a single Gigabit LAN. But if you are expecting upto 4 users then I'd imagine you were planning on LACP with dual NICs. Which then means the disks will not fully saturate the links.

I'd go with RAIDz for data integrity. However if this is a media server as well, RAID 5 maybe the better option, purely for speed. Unfortunately if the RAID card fails then and you can't get an identical RAID card, you lose all your data, unlike a ZFS where you can move the disks to new motherboard and still get the data.