It is deceptively easy to jump on the solid state bandwagon. What’s not to like? It is very compact, very fast, relatively shock resistant, and could be tweaked to use less energy. Sounds great, right? Then why haven’t all IT departments, data centers, and other storage hungry data facilities made the switch to solid state? However, given the realities on the ground, we won’t be saying good-bye to the current system of tiered storage. Instead of hard disk caching and tiering, we would need solid-state tiering. Still, tiering will be here to stay. Why? Two words: durability and performance. Unless all SSD drives in the world are made by one manufacturer, there will be differences in performance and unit durability among differing makes and models. That is the reality.
SSD Tiering is needed to address these differences. Different SSD types differ among performance capabilities. For example, RAM-based SSD drives outperform Flash-based SSD drives on both the reading and (particularly notable) writing front. Even within these large subdivisions of Flash and Ram are differences. For example, in Flash-based SSD drives, there is a big difference between eMLC (enterprise multilevel cell) flash SSD and SLC (single level cell) flash SSD. EMLC writes data slower because it tries to improve its durability compared to the faster but more expensive SLC.
In addition to writing and reading speed are differences in durability. This is the quality that breaks down solid-state drives into different tiers. In terms of durability, DRAM comes out on top. However, this type of SSD is very susceptible to power surges and power losses. It is quite volatile and needs lots of monitoring. Flash, as a whole, is comparatively less durable than DRAM. However, within the range of flash SSD offerings, there is quite a spectrum in terms of durability. SLC is the most durable, and it has the longest lifespan. It is also more expensive. The cheapest flash SSD is also the shortest-lived: the TLC (triple level cell).
Due to the different prices, types, and durability of SSD drives, there will always be a need for caching and tiering. There will always be a need to manage the different tiers. While the day will come when whole data centers will be SSD-based, it will take longer for such a data center to be completely free of tiered management. Tiering and caching are here to stay.