Decided to Build my own NAS solution , any advice/recommendation will be helpful .

I'm a systems admin, and was the test lab systems admin at a company that makes backup storage products. I just wanted to set that up for credibility purposes, so you know I know what I'm talking about.

1. That memory guideline is just that, a guideline. It shouldn't hurt you to have a little off from 1GB/TB on a storage server. All my storage servers are far off from that ratio. It is more important to keep in mind the number of users per GB of memory. 4GB of memory could be fine for a storage server if you only have one thing being accessed at a time.

Getting into data deduplication, though, gets more complicated. If you want dedup on your data, then you do need 1.25GB+ per TB of data stored. I think that is the root of the recommendation for FreeNAS.

2. I've tried FreeNAS, and found that using CentOS is far easier to administrate. It takes some research to do it either way, but I was able to get CentOS to work in a little over an hour with an NFS share and about 3 hours with a CIFS share, and couldn't get FreeNAS to work with either in over 2 days of fiddling with it. The web interface for that just made no sense to me, and too many different things had to be set up to get it going. I made a user account for access, then made the share, and then set the rights, but it still wouldn't let me access the share at all. It was just a big PITA. CentOS was much easier.

3. I always recommend HGST's Ultrastar line. They're enterprise/server level drives, and the best of those level drives in both performance and reliability, but they do cost a good bit more. If you don't want to spend that much, WD's Red line is pretty reliable. Avoid Seagate or Toshiba. Don't even try to make a RAID from WD's blue or black lines. WD blue and black lines simply won't work with RAID. WD's Gold line is the enterprise level RAID drive, and pretty much just relabeled HGST Ultrastar drives. WD's old RE3 line is still very good, even if they're old drives. They're quite reliable.

Seagates will, but they aren't very reliable. Even Seagate's enterprise line is not reliable. In my last job, I had over 6000 Seagate drives, and had to replace about 10-12 per week. The first shipment of 6TB SAS drives we got had over a 30% failure rate over the first 3 months. I had to replace 6 drives of 24 in the first 2 weeks of the project, and another 3 drives in the two months after that. Once we went from prototype phase into testing phase, of the 348 drives (29 trays spread across 10 test systems), I had to replace 120 of them within the first 2 months of the project. They claimed it was a firmware problem that they fixed. After that, though, the remaining drives didn't fail at all for the next 18 months. I left that job at that point, so I don't know how well they've done over the last 9 months. Toshibas were about as bad, but we had a way smaller sample size at about 800 in the lab.

The HGST drives we had were absolutely great for reliability. I had trays of 500GB Hitachi drives dating back 12 years that were still going strong with no failures. The 4TB drives we got also had no failures while I was there. Of course, the sample size was smaller at about 2000 Hitachi drives, but I think I had a total of about 5 or 6 fail in the entire 6 years I worked there. I'm a HGST convert for life after that job. I currently have 6 4TB Ultrastar drives in a RAID 10 for my storage at home.

At my current job, we have WD Black drives in a Linux software RAID for my backup storage. Obviously not my first choice, but they work, so I can't really do anything about it.

4. Gigabit will cap at 112.5MB/s transfer rate with normal frame size. With jumbo frames, you can get up to 118MB/s, but jumbo frames can be tricky to set up. You can try bonded links, depending on your OS, but the most you'll get from a single stream is the same 112.5MB/s. It takes multiple streams to utilize bonded links, and most operating system functions don't use multiple streams. Most modern hard drives can saturate that easily. RAIDs will certainly do so.

With the new 2.5Gb/s and 5Gb/s network adapters coming out, you might have a chance to upgrade that later. I'm running 10Gb/s with a $400 switch I found, a Dlink DGS-1510-28X, and $100 NICs I got throug my last job, Qlogic QLE3242-SR. I got them at a discount directly from the manufacturer, as they were old models. I've seen those NICs listed on Ebay for about $100-120 with optics. They do need direct cooling, though. 10Gb isn't as expensive as it used to be. It's actually doable at home now.

1. For 4 systems, 4-8GB would work just fine. You have 16, so that is more than enough. No problems there.

2. I'd advise something a little beefier than that one. Go for a good name brand switch, and not one of the little $20 models. They're cheap for a reason. saturating all the links on something like that would probably give you about half the performance you'd expect, and probably some latency issues. A good Netgear or Asus switch at about $35-40 would do better. The switch inside a router is about the same situation. Get a cheap router, and you get a cheap switch with it. Saving $20 on a switch that you have to replace after a year isn't really saving money over a $40 switch that will last a decade.

3. Use what you prefer and can use. Try out FreeNAS and see how well you can work with it. Maybe you'll do better than I did. It depends entirely on your skills. I was just saying I had a hard time with FreeNAS. You may have an entirely different experience.

Whatever works for you. Just keep that in mind.