Bill Roth, Ulitzer Editor-at-Large

Bill Roth

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An Introduction to ZFS: The ZFS Info Center

For more than a decade, storage system performance has remained rather stagnant while drive capacities and application performance demands steadily have increased. The result of this trend is an expensive problem: Storage users are forced into buying expensive hard disk drives (HDDs) to get a moderate performance boost (by reducing I/O latency) and/or forced into over-buying capacity in order to meet performance requirements. With the advent and decreasing price of flash, storage vendors are integrating it into their products to solve this problem. Nexenta’s ZFS technology is leading the industry in its ability to automatically and intelligently use flash in a storage system that offers the appropriate capacity and performance capabilities at a total cost that is dramatically lower than most legacy storage systems (and even still lower than legacy vendors who have begun to use flash as well).

The Parts of a ZFS Hybrid Storage Pool

In a ZFS Hybrid Storage Pool (HSP), there typically are three varieties of hardware—DRAM, flash, and spinning HDDs, with flash being used in two distinct ways. The following sections explore each of these.

ZFS logo
Adjustable Replacement Cache (ARC): The ARC (sometimes known as the “Adaptive” Replacement Cache) lives in DRAM. It is the first destination for all data written to a ZFS pool, and it is the fastest (i.e., lowest-latency) source for data read from a ZFS pool. When data is requested from ZFS, it looks first to the ARC; if it is there, it can be retrieved extremely fast (typically in nanoseconds) and provided back to the application. The contents of the ARC are balanced between the most recently used (MRU) and most frequently used (MFU) data.

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Bill Roth is a Silicon Valley veteran with over 20 years in the industry. He has played numerous product marketing, product management and engineering roles at companies like BEA, Sun, Morgan Stanley, and EBay Enterprise. He was recently named one of the World's 30 Most Influential Cloud Bloggers.