These days, businesses deal with vast amounts of data, and the pace of data generation is growing, from AI pipelines and digital content to compliance records and analytics. As the need for storage grows, so does the need to find a balance between cost and performance.
This is where tiered storage comes in. By sorting data by how often it is accessed and how sensitive it is to latency, businesses can choose the best storage media for each use case. In this context, warm data stands out as the most significant and important tier in terms of money. It is used a lot, but not immediately, and it makes up a substantial portion of the workloads for persistent storage.
The question is: where should warm data live? Western Digital says the answer is clear: on hard disk drives (HDDs). Modern HDDs are the best choice for warm-tier workloads because of their cost, growth ability, and performance. Brad Warbiany, Director of Planning & Strategy at Western Digital, says, “Using SSDs for warm data is like moving into a house across town using a sports car instead of a moving truck. It’s fast, but it’s not the best or most cost-effective tool for the job.”
- The Rise of Warm Data: Scale Without Deletion
- Why SSDs Don’t Scale for Warm Data
- The TCO Equation: More Than Just Drive Price
- Western Digital’s Purpose-Built HDD Architecture
- Seamless Integration with Modern Storage Architectures
- Eliminating HDD Performance Myths
- The Road Ahead: HAMR and Beyond
- Conclusion: HDDs Are the Infrastructure Backbone
The Rise of Warm Data: Scale Without Deletion
In 2024, the total amount of data created, captured, copied, and used worldwide was 149 zettabytes, and will reach more than 394 zettabytes by 2028. But what’s even more critical than total volume is data composition. Enterprise data is not uniformly accessed:
- Hot data requires sub-millisecond latency and high IOPS.
- Cold data is rarely retrieved and is best suited to archival media like tape.
- Warm data, however, is frequently accessed but not latency-critical.
Brad explains, “Warm data is where most value is today. Think about a social media post that is hot for a few weeks and then warm forever. The same logic applies to video, analytics logs, and AI training sets.”
This data is retained for long periods, often indefinitely, especially as AI makes historical datasets newly relevant. As a result, the warm tier is not just growing, it’s exploding.
Why SSDs Don’t Scale for Warm Data
At first glance, SSDs seem like the obvious choice for any active data. But the economics of flash storage simply don’t hold at the petabyte scale.
Brad notes, “The price per terabyte for HDDs is about 6x lower than that of SSDs today, and that ratio has held steady for over a decade.”
Cost Comparison: HDDs vs SSDs
To illustrate this disparity, here’s a side-by-side comparison of typical enterprise HDDs and SSDs across key metrics that matter at scale:
| Metric | HDD (HelioSeal + UltraSMR) | SSD (QLC NAND) |
|---|---|---|
| Capacity | 20–32 TB | 15–122.88 TB |
| Cost per TB | $12–18 | $75–100 |
| Watts per TB (Idle) | ~0.2 W | ~0.04–0.2 W |
| Sequential Throughput | ~270 MB/s | ~500 MB/s (SATA/SAS), up to ~7,000 MB/s (NVMe) |
SSDs offer slightly lower idle power in some scenarios, but countering any marginal energy savings is their acquisition cost. Enterprise SSDs often remain powered 24/7, negating the low-power benefits seen in consumer-grade flash.
As Brad summarizes, “When it comes to total cost of ownership (TCO), the deciding factor isn’t performance, it’s cost per bit. SSDs are faster, but warm-tier workloads don’t need that speed.”
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The TCO Equation: More Than Just Drive Price
Understanding TCO requires a broad view of storage economics. While many discussions around SSDs highlight potential energy or cooling savings, these secondary factors pale in comparison to acquisition costs — especially at petabyte scale.
Brad emphasizes, “Power and cooling can contribute to operational cost, but they’re small levers. The overwhelming driver of TCO is $/TB, and that’s where HDDs consistently outperform.” In high-density data centers, the economic argument is clear: HDDs are purpose-built for warm-tier workloads that prioritize capacity and cost over sub-millisecond access.
TCO Contributors for Warm-Tier Storage
The table below breaks down the major contributors to TCO and highlights where HDDs maintain a strategic edge for warm-tier workloads:
| Category | Contribution to TCO | HDD Advantage |
|---|---|---|
| Total Acquisition (Drive + Compute) | High | Strong (4x cheaper) |
| Power & Cooling | Medium | Moderate SSD advantage (lower power), but not enough to outweigh higher cost |
| Rack Density | Low to Medium | Capacity-dependent (high-capacity QLC SSDs may surpass HDDs in density) |
| Maintenance/MTBF | Low to Medium | Workload- and configuration-dependent (QLC SSDs may match HDDs in maintenance efficiency) |
Western Digital’s Purpose-Built HDD Architecture
Western Digital has engineered its drives with technologies that improve capacity, reliability, and efficiency to make HDDs even more effective for warm data. These include:
UltraSMR
An evolution of Shingled Magnetic Recording (SMR), UltraSMR uses advanced encoding to increase track density without requiring changes to the software stack.
- Benefit: Up to 20% more capacity per drive than CMR.
- TCO Impact: Same cooling, same power, more bits per rack.
HelioSeal
Drives sealed in helium instead of air reduce friction and allow for more platters in the same form factor.
- Benefit: Higher capacity with lower vibration and energy use.
- Platform Milestone: Now shipping with 11-disk configurations, up to 32 TB capacity.
ePMR and Triple-Stage Actuator
Energy-Assisted Perpendicular Magnetic Recording (ePMR) enhances write head stability, and triple-stage actuator technology improves seek precision. The result is better sequential throughput and reduced write error rates.
- Benefit: Sustained 290+ MB/s sequential reads.
OptiNAND & ArmorCache
These firmware-level technologies use embedded flash to buffer metadata and write caches, improving drive responsiveness even in write-cache-disabled environments. At its launch, ArmorCache was the first technology to offer enterprise power-loss protection in write cache-enabled mode for HDDs.
Brad explains, “All of our drive innovation points toward one goal: optimizing for warm-tier workloads where cost and scale matter more than microsecond latency.”
Seamless Integration with Modern Storage Architectures
Western Digital designs its HDDs to integrate tightly with software-defined storage (SDS), object storage, and cloud-native infrastructure.
Object stores like Ceph and MinIO are often configured for sequential read/write patterns, which is exactly what HDDs excel at.
Moreover, UltraSMR drives are designed as drop-in replacements for standard SMR drives, requiring no software refactoring. “If you’ve already made the software changes to enable SMR, UltraSMR is a seamless way to adopt more capacity without rewriting your stack,” Brad notes.
Even hyperscale platforms, which require high IOPS and scalability, balance SSDs for metadata and caches with HDDs for bulk warm data. This hybrid model delivers the best of both worlds.
Eliminating HDD Performance Myths
Some people think HDDs are slow, but that’s not true. Today’s enterprise HDDs can attain throughput rates of up to nearly 300 MB/s, which is enough for warm-tier workloads.
Brad says, “Calling HDDs slow is like saying an Olympic marathon runner is slow because they can’t run as fast as Usain Bolt.” HDDs are the best in terms of endurance and storage size.
The Road Ahead: HAMR and Beyond
Western Digital is investing in heat-assisted magnetic recording (HAMR) to increase area density even further and lower the cost per terabyte.
HAMR is a new turning point for HDDs. It lets them hold even more data without using more power or space. This new idea will make HDDs even more dominant in the warm tier for a long time.
Conclusion: HDDs Are the Infrastructure Backbone
Warm data isn’t a niche; it makes modern enterprise storage work. It powers AI, compliance, analytics, and collaboration. As companies keep more of it for longer, the need to grow in an affordable and long-lasting way only gets stronger.
Western Digital’s HDDs combine high capacity, strong performance, and among the best total cost of ownership for warm-tier workloads, thanks to innovations like UltraSMR, HelioSeal, and ePMR. Far from being outdated, today’s HDDs are the result of decades of technological advancement, making them remarkably efficient, reliable, and well-suited to the majority of business data needs. For most workloads, HDDs offer the perfect balance of scale and value; while SSDs, much like a sports car on a racetrack, are best reserved for those specialized, high-performance applications where only the fastest speeds will do.
Brad Warbiany says that cloud architects already know this. The smart people are making their architecture fit the needs of their workloads, not the hype. HDDs still power nearly 80% of the world’s data center capacity because they work.
If your storage strategy doesn’t clearly distinguish between hot and warm data, it’s time to rethink it. The benefits are significant cost savings, long-term sustainability, and infrastructure that grows with your data instead of against it.
Look through the Western Digital Ultrastar DC HC600 series to find the best warm-tier storage strategy for your performance, cost, and growth needs.