Please stop the madness: The Mac's Fusion Drive isn't about caching

The words "caching" and "Fusion Drive" keep being used in the same sentence, or in the same paragraph. This is all wrong, so please save that cache reference for another day and another product.

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.

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