Calculating SSD useable life in embedded medical equipment applications

Embedded systems demand some of the toughest storage requirements embedded designers must fulfill. Solid-State Drive (SSD) technology has advanced to meet high end-user and embedded system OEM expectations for storage in terms of capacity, performance, reliability, longevity, and low total cost of ownership. Gary presents a new metric to measure SSD technology and emphasizes the importance of using SSDs with drive useage monitoring to prevent medical device failure.

SSDs have evolved to become a viable option to replace rotating Hard Disk Drives (HDDs) in many Embedded Systems, including medical equipment. This is because SSDs eliminate the single largest industrial computer mechanism in most medical systems – the moving parts of HDDs.

Medical devices have long product test and network appliance qualification cycles and are subject to rigorous regulatory approval processes. These processes are necessary given that primary hard drive failure is an unfortunate reality in all devices, not just medical devices; it is not “if” but “when” an HDD will fail because it has moving parts that at some point will wear out and stop functioning. When failure occurs, it can be a regulatory nightmare.

The Safe Medical Device Act of 1990 authorizes the Food and Drug Administration (FDA) to regulate medical devices. Hospitals and health care organizations must report all network appliance failure causing serious illness, injury, or death. This can result in costly lawsuits, product recalls, and untold ill will. Even if there is no fatality, at the very least, the Industrial computer device will have to be requalified through the FDA, which could take years and cost hundreds of thousands of dollars.

Storage solutions must be rugged and able to perform in critical applications without failure. A small footprint is often required, as well as tolerance to high shock and vibration and protection against drive corruption from power disturbances caused by user error or environmental conditions.

In addition to these requirements, medical equipment designers face continued pressure to reduce overall system costs in medical equipment. NAND flash components have advanced to deliver lower cost per bit, but in doing so, have sacrificed reliability and endurance. This has led many OEMs to question how long an SSD will last in their critical medical applications.

To help industrial computer designers address this significant industry concern, the following discussion provides a brief overview of recent changes in NAND flash technology and some of the algorithms SSD vendors use to manage those changes. Using this common data, a new network appliance methodology can help designers predict useful life by outlining the parameters that SSD manufacturers control (such as the type of NAND used, write performance, and write amplification) and those that system OEMs can control (usage model, capacity, and write duty cycle).

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