Keeping in mind that the best server and storage IO is the one that you do not have to do, then second best is that which has the least impact combined with best benefit to an application. This is where SSD, including DRAM- and NAND-flash-based solutions, comes into the conversation for storage performance optimization.
The question is not if, but rather when, where, what, and how much SSD (NAND flash or DRAM) you will have in your environment, either to replace or to complement HDDs.
Solid-state devices (SSDs) are data storage memory (Figure 1) mediums that utilize semiconductor based memories as opposed to magnetic media found in hard disk drives (HDDs) or magnetic tape. Semiconductor memories include ultra fast volatile dynamic random access memory (DRAM) commonly found as main memory (e.g. RAM) in servers along with and non-volatile memory (NVM) typically NAND flash. Nand flash based SSDs can be found in cameras (as SD cards), cell phones, iPods, and PDAs, as well as in notebooks, net books, laptops, tablets, and workstations. SSDs are also appearing in larger servers, appliances, and storage systems from consumer to enterprise level.