Don't opt for half-mesures; go for the real thing:
SuperMicro SC847BE2C-R1K28LPB. Yes,
it is ~2000U$, but it comes with two LSI expanders and it has the widest modern motherboards compatibility list and supports SAS 12G. The cost of the chassis won't be a big factor on the overall price. 700$ (over
that one, which only supports SAS 6G and 24 drives) is marginal when you consider the entire system cost. Plus, opting for a 36-drive chassis over a 24-drive one will make the "NAS" last longer before it's filled up, delaying an upgrade and saving you money on the long run.
You probably don't want SATA drives anyway, because the IOps suck in large arrays. SAS 12G drive aren't that much more expensive, unless you compare them with cheapo drive with lower reliability figures, which you wouldn't want in such a large array anyway (increased risk of failure and array-corrupting errors).
6TB drives are the best capacity for the buck at the moment, but the newer 8TB Enterprise Capacity from Seagate offer the most throuput. HGST Helium drives are simply too expensive.
So:
- SuperMicro SC847BE2C-R1K28LPB (2030$)
- SuperMicro MCP-220-82609-0N (44$) - to put your SSD boot drive RAID 1 array or your tier 1 storage
- SuperMicro MBD-X10DRH-CT (665$) - has two 10GbE ports and integrated LSI 3108 SAS 12G controller
- 2x SuperMicro SNK-P0048AP4 (30$ - 2U active heatsink
- 2x Intel E5-2600 v4 CPU of your choice - they will be out in less than 3 months, so no point buying a v3 now.
- 8x or 16x DDR4 2400MHz ECC Reg RAM stick of your choice (E5-2600 v4 can use up to 2400MHz frequency memory and they shouldn't be much more expensive than 2133MHz sticks)
- 2x 2.5" SSD of your choice - to go in the 2-drive cage above
- 36x 6TB or 36x 8TB SAS 12G LFF of your liking (will cost between 10,542$ and 18,185$)
For 36x 6TB drives, I'm at 13,341$ without the SSDs, CPUs and RAM sticks. For the 36x 8TB drives, without the same parts, I'm at 20,984$. Even with a single low-end CPU and 4 sticks of RAM, you'll hit close to 1000$. The 2 SSDs should cost you at less 300$, so the lowest you can build this is almost 15K$. You can easily hit 30K$ if you crank the CPU and RAM. But in both cases, you won't need an upgrade for a LONG time.