As next-generation medical devices migrate to smaller form factors and faster host-system interfaces, the storage system must follow suit. The positive result of this trend is the emergence of more reliable medical applications with more capability than ever before.

These advances, however, come with a new set of concerns, such as drive reliability, lifespan, endurance, usability, and the potentially adverse effects of power disturbances. As a result, choosing the right type of storage for a particular medical device is increasingly more complex.

Solid-state storage has advantages of high reliability and performance, scalability, security, and endurance. But not all solid-state storage is created equal. For example, traditional flash-card technology, originally developed for consumer applications, appears similar but may not stand the rigors of the medical industry.

For instance, it's common to see medical devices used in rest homes, paramedic vehicles, and aircraft. This growing trend makes it possible for people to play a greater role in maintaining their own health outside of a hospital or technician's immediate supervision.

Solid-state storage has several advantages over traditional storage devices for these applications. For instance, solid-state storage has no moving parts, a benefit for rugged or mobile environments. Medical equipment using solid-state storage is not susceptible to normal shocks or vibration.

Rotating hard drives, on the other hand, with moving actuator arms have a greater chance of malfunctioning when bumped or moved suddenly. Hard-disk drives have lower temperature and altitude tolerances as well, factors that come into play more as medical equipment is deployed in mobile environments such as airplanes and life-flight helicopters.

Trends now also call for medical devices to be as small and portable as possible. Operating rooms in particular, are requiring that more equipment fit into less space which translates into physically smaller and lower-power medical devices. This means designers must find a storage device that offers performance, consumes little power, and scales to fit future needs.

Rotating hard drives are confined largely to 3.5, 2.5, and 1.8-in. form factors. Solid-state storage, on the other hand, is more flexible and can be deployed in a number of smaller industry-standard form factors such as CompactFlash, USB, or 1.8-inch drives. Because solid-state storage also consumes little power, it increases performance and extends battery life. For instance, traditional small hard drives consume about 2.5 W, while the average solid-state runs on less than 0.2 W, about 8% of the hard drive.

The four big plusses for solid-state drives over others include tolerances to power irregularities, lifespan, device diagnostics, and endurance.

Power irregularities, common even in hospitals, can corrupt a data-storage subsystem. About two-thirds of field storage-device failures are due to power disruptions. Spikes, brownouts, surges, and blackouts are especially worrisome when it comes to healthcare because they cause improper operations in medical devices or they cease functioning altogether. Other storage design considerations include how power anomalies affect data integrity with the common practice of devices suddenly switched off and on, frequent alternation between ac and battery backup power.

During under-voltage situations, there may be insufficient power for the medical device and memory components, letting the host system send data which corrupts the drive. Advanced solid-state storage solves that problem with voltage-detection circuitry that senses power problems. At a low-voltage threshold, the drive sends a busy signal to the host system ceasing transmissions until the power level stabilizes. Then address lines can be latched, which ensures writing data to a proper location. This prevents sector overwrites which cause drive corruption. This is critical for medical devices that run on low power.

The lifespan of medical equipment can be many years, often in less-than-the-best conditions. What's more, many medical devices require approval from the FDA, so forced changes or upgrades may require costly reevaluations or recertifications that delay their entry to the market.

Internal diagnostics refers to how well the storage unit detects anomalies from wear and aging. Advanced solid-state storage uses Self-Monitoring Analysis and Reporting Technology (SMART) which lets users monitor the exact amount of usable storage left in a drive. This monitor accurately forecasts when a potential failure will occur and allows time for repairs, thus avoiding unexpected failures which can lead to critical or life-threatening situations.

Traditional flash cards, on the other hand, run until they fail, often suddenly and without warning. This leads to maintenance calls, the loss of data, and potentially life threatening emergencies.

Endurance of a solid-state drive depends on storage media, wear-leveling, and error correction codes (ECC). Advanced solid-state storage optimizes all three of these elements. The most advanced storage media available has maximum endurance and performance to meet critical medical requirements. Advanced ECC algorithms should provide exponentially better error correction than standard versions used in consumer products. And proprietary wear-leveling algorithms evenly distribute wear over the entire solid-state drive.

A COMPARISON OF WIDELY-USED STORAGE DEVICES FOR MEDICAL EQUIPMENT

MARKET CONCERN	HARD DRIVE	FLASH CARD	ADVANCED SOLID-STATE STORAGE
Corruption due to power disturbances	Adequate	Susceptible to power anomalies	Integrated voltage circuitry protects against power anomalies
Product lifecycle	Less than one year	Less than one year	Multi-year
Wear-out	Environmental and mechanical concerns	Write/erase endurance <10K cycles	Write/erase endurance exceeds 2M cycles
Ability to forecast useable life	SMART available, but has limited warning capability	None	SMART
Frequent costly product requalifications	Yes	Yes	No. Qualifications not forced by product obsolescence
Security options	Basic password encryption	Possible password	Multiple user selectable security options
Power consumption	2.5W	0.2W	0.2W
Mechanical dimensions (in.)	2.5, 1.8, 0.8	2.5, 1.8, CF, SD, Micro SD	2.5, 1.8, CF, PC, 40-pin
Designers should evaluate storage devices based on their ability to handle power anomalies, provide ample endurance to perform in products with multi-year lifecycles, accurately forecast usable storage life, offer enhanced security, and provide highly reliable storage management technology.