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Why and how to implement NVMe power management

By John Edwards

Fast, reliable NVMe SSDs have revolutionized data storage. There's a downside to NVMe SSD technology, however: high power consumption.

Fortunately, the NVMe specification offers numerous power management features. Here's what you need to know.

Why NVMe power management is important

NVMe power management is necessary to achieve an acceptable balance between platform thermals and total power consumed by the SSD. Even though the form factor defines maximum power for an SSD, the host can use NVMe power states to change the amount the SSD consumes, said Imran Hirani, director of product architecture for Taiwan-based enterprise SSD manufacturer Phison Electronics Corp. That change is based on the desired access pattern, as well as the maximum available thermal solution and airflow for the system.

"Client drives use nonoperational power states to achieve longer battery life, as client drives are idle most of the time," Hirani said.

Key power management technologies and features

A host can access NVMe power management features in three different ways:

• To set the power state conditions for the Autonomous Power State Transition feature, use the set feature command (FID=0xC, APST). The SSD will then transition to different power states based on the set condition.
• Use the set feature command for power management to change a current SSD power state.
• Use the set feature command for host-controlled thermal management to establish two temperature thresholds. The device will automatically transition to the lower power state once it reaches the set temperature.

Best methods for using NVMe power management

NVMe power management is based on the workload and the available thermal platform. It will vary between client, data center and enterprise SSDs.

"For client SSDs, since the drive is idle most of the time, APST NVMe power management is the best method, as the drive will transition to a lower power state based on the set idle time limit," Hirani said.

Data center SSDs, meanwhile, typically use the NVMe power management feature to limit maximum SSD performance for specific workloads to achieve balance between performance and thermal budget requirements.

"Since enterprise SSDs are active most of the time, they can use the thermal management feature to make sure the device doesn't overheat and trigger the thermal shutdown condition," according to Hirani.

NVMe power risks

NVMe power management features find acceptable balances between power, performance, product reliability and customer experience. However, there are risks if organizations don't properly configure NVMe power management. They include the following:

• Failure to properly manage the SSD's active power can lead to excessive heat generation, which potentially leads to a level where available system airflow will not be able to sufficiently cool the SSD. "In worst cases, the SSD can reach its thermal shutdown limit and will shut down," Hirani said.
• When in the nonoperational power mode, a drive that fails to transition to lower power modes will continue to draw power even through the drive is idle. "This will drain the battery in the laptop/notebook faster, leading to a poor customer experience," Hirani warned.
• While NVMe power states provide various power-saving levels, there's also a tradeoff in the time it takes to enter and exit each state. "The lowest power state will take the longest to enter and exit," Hirani said. "Not considering the enter and exit latency could lead to lower performance or longer response time."