SMR Drives vs. Traditional HDDs: Which is Greener and Why?

Host-managed Shingled Magnetic Recording (HM-SMR) drives offer an alternative to traditional Conventional Magnetic Recording (CMR) drives by overlapping data tracks to achieve greater areal density. This results in higher storage capacity on the same mechanical platform. Combined with their sequential write model, HM-SMR drives reduce energy consumption by avoiding seek-heavy operations. This article examines why HM-SMR drives like the Western Digital Ultrastar DC HC690 are greener than their CMR counterparts, such as the Ultrastar DC HC590, for the same generation.

Capacity and Power Efficiency 

Western Digital’s HC590 (CMR) and HC690 (HM-SMR) drives are based on the same 11-disk, 7200 RPM HelioSeal platform. The HC590 provides 26 TB of capacity, while the HC690 offers 32 TB – a 23% increase in capacity without significant changes to mechanical design.

Idle power for the HC590 is approximately 5.6 W, and for the HC690 it is around 5.5 W. With the slightly lower power draw, the HC690 achieves a significantly lower watts-per-TB ratio:

• HC590: 5.6 W / 26 TB ≈ 0.22 W/TB
• HC690: 5.5 W / 32 TB ≈ 0.17 W/TB

This means the HC690 is about 20% more efficient in terms of watts-per-terabyte, allowing storage systems to achieve the same capacity using fewer drives and with reduced power consumption.

Sequential Access and Reduced Seeks 

HM-SMR drives require data to be written sequentially in zones, which reduces the frequency of mechanical seek operations. These seeks are among the most energy-intensive actions performed by a hard drive. In contrast, CMR drives are optimized for random access workloads, which trigger frequent seeks and higher instantaneous power usage.

By minimizing seek operations and focusing on sequential access, HM-SMR drives maintain a steadier, more efficient power profile during operation – ideal for cold or archival storage.

Environmental Considerations 

Over time, reduced power usage per terabyte contributes to lower energy bills and a smaller carbon footprint. For example, running a HC690 drive continuously over a year (5.5 W average) consumes about 48.18kWh. Distributed over 32 TB, this results in ~1.51 kWh per TB-year. Using a global average CO₂ intensity of 0.4 kg/kWh, this equates to approximately 0.60 kg CO₂ per TB-year.

Compared to a HC590 drive (5.6 W / 22 TB = 1.89 kWh per TB-year), the HC690 delivers better sustainability performance, especially at hyperscale deployments.

Conclusion 

HM-SMR drives like the Western Digital HC690 offer a greener alternative to CMR drives by combining higher capacity with lower per-terabyte energy use and fewer mechanical operations. While best suited for cold and sequential workloads, their energy efficiency benefits can be substantial at scale. For IT planners and infrastructure designers aiming to optimize both cost and environmental impact, HM-SMR is a smart long-term investment.

Author: David Gerstein
David Gerstein is the CTO of Leil, an Estonia-based storage infrastructure company building HDD-native software for the exabyte era. Leil is in active co-engineering partnership with Western Digital, validated across the WD, Seagate, and Toshiba drive ecosystems.