New-Tech Europe | September 2016 | Digital Edition

Extending Product Lifespan Using Wear-Leveling

Datalight Staff

Introduction: Keeping Up with the Data Deluge Over the past 20 years, flash memory hasbeenwidelyadopted inmainstream consumer grade products with relatively short lifetimes, sometimes measured in months, as well as more industrial and commercial devices with lifetimes of years or decades. There are many unique characteristics of flash memory that have fueled its growth across these different market segments, such as its ability to retain data when power is interrupted. Unfortunately, flash technology has the downside of finite lifespan and lower endurance. Complicating the issue is the fact that hardware and software technologies designed to improve flash life often take a backseat to other seemingly more pressing issues of system design. This paper discusses the factors that

The second metric, endurance cycles, is a measure of the number of write and erase cycles that the flash memory can endure before becoming unreliable. Flash memory is organized into a number of erase blocks or sectors, and each must be erased prior to writing data. A typical erase block is 128KB in size, however depending on the flash part, it may range from 512B to 4,096KB or even more. A given address within an erase block cannot be rewritten without first erasing it. Erase cycles are cumulative and affect only those erase blocks being cycled. In other words, an error in any erase block is constrained to the data of that block. Erase cycles of SLC flash range from 1,000 to 100,000. While these ranges have an order of magnitude difference, it is the application the

determine when limitations of flash memory lifetime become significant, and presents test data for several common wear-leveling options in Linux. Flash Lifetime Metrics Flash memory lifetimes are described in two primary metrics which are generally touted on the first page of any flash manufacturers’ data sheets: • Data retention • Endurance cycles Data retention is often listed at 20 years for a given operating temperature range. Increased temperature ranges reduce the data retention period which further decrease as the flash memory is used at or near the limits of its specified operating temperatures range. It is important to note that data retention is measured from the time data is successfully programmed.

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