It is hard to believe that we are essentially at SSD-HDD price parity? Of course I am comparing enterprise class 10K/15K HDDs to consumer grade SSDs. Below are prices I am seeing
600GB 15K 3.5in HDD $370
3TB 7.2K 3.5in HDD $400
300GB 15K 2.5in HDD $370
900GB 10K 2.5in HDD $600
1TB 7.2K 2.5in HDD $230 (less for consumer HDDs)
512GB SATA SSD $400-600
Intel SSD DC S3700 400GB $940
The 512GB SATA SSDs are consumer grade, MLC NAND, with only 7% over provisioning.
That is 512GB (1GB = 2^30) of NAND, with 512GB (1GB =10^9) of user capacity.
Intel just announced the SSD DC S3700, which appears to be a reasonable enterprise product, in having 32% over-provisioning. I am inclined to think that DW permanent data does not need more over-provisioning than in the consumer grade SSDs. Otherwise your db is probably not a DW.
Potentially tempdb might need more write endurance than in the consumer SSDs. So the question is whether a large array of consumer SSDs supporting mostly static data and a smaller write intensive tempdb is a good match.
Most SAN vendors are peddling grossly over-priced enterprise grade SLC SSDs. That is because they want SSD to be used for caching or tiered storage, which results in heavy write activity. Apparently SAN vendors have no concept of DW.
Now if we could only get system vendors to provide storage bays for 9.3mm SSDs instead of 15mm 10K/15K HDDs to achieve higher density. Better yet, arrange with SSD vendors to ditch the case, providing the SSD on just the PCB. The SSD storage bays should also be more appropriately balanced, say 2 x4 SAS ports to 8-bays.