There was some hubbub surrounding the release of machines with Apple's Fusion Drive Core Storage-based management software. And much confusion. The word "caching" crept into the stories and posts. The caching label appears to be sticking and that is incorrect.
I ran a search for "Fusion Drive" and "caching" and found plenty of recent stories that describe the Fusion Drive as managing caching for a performance boost. Not.
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Instead, it's an implementation of storage tiering. This was described in a non-Apple, server-market context in a Wednesday announcement by SSD technology vendor Enmotus. The company is calling its automated data migration solution "micro-tiering."
"Let's clear up any remaining misconceptions that tiering and caching are synonymous," said Mark Peters, senior analyst at the Enterprise Strategy Group. "They are quite different: tiering essentially creates a virtual pool of available storage, and moves the most frequently accessed or more active data to the faster tier - which in Enmotus' case is flash, with the solid-state capacity being additive to the overall storage pool.
Tiering is unlike caching, because the latter simply creates a temporary copy of the most accessed or active data in the cache; with tiering, the SSD operates as primary storage with no requirement to 'flush' the cache, which means less overhead and lower wear on the solid-state.
So, not caching. Tiering.