CMR, SMR, and Other Confusing Things About Hard Drives

What are these technologies, and why should you care?

When shopping for hard drives, you might notice acronyms like “CMR” or “SMR” in product descriptions. These refer to different recording technologies used in hard drives, and they can significantly impact your drive’s performance depending on your use case. At PricePerGig.com, I tag drives with these technologies to help you make informed purchasing decisions.

The Technologies Explained

CMR (Conventional Magnetic Recording)

CMR, sometimes called PMR (Perpendicular Magnetic Recording), is the traditional recording method used in hard drives for many years. In CMR drives, data tracks are written parallel to each other without overlap. This makes CMR drives:

• Better for random write operations
• More suitable for RAID arrays and NAS devices
• Generally more versatile for most use cases

SMR (Shingled Magnetic Recording)

SMR is a newer technology where data tracks partially overlap like shingles on a roof. This allows manufacturers to pack more data into the same physical space, increasing capacity at a lower cost. However, SMR drives have some drawbacks:

• Slower performance for random write operations
• Potential compatibility issues with some NAS systems and RAID configurations
• Better suited for archival storage or read-intensive workloads

HAMR (Heat-Assisted Magnetic Recording)

HAMR is an advanced technology that uses a tiny laser to heat the disk material momentarily as data is written, allowing for even higher data density. Currently, HAMR is primarily seen in enterprise-grade drives with very high capacities (20TB+).

ePMR/EAMR (Energy-Assisted Magnetic Recording)

ePMR or EAMR is a technology used by Western Digital to increase platter density. It’s similar to HAMR but uses a different energy-assistance method. EAMR drives are generally compatible with most systems and offer good performance.

How PricePerGig.com Determines Drive Technologies

The website applies CMR, SMR, and HAMR tags to drives based on a carefully researched set of rules. Here’s how I do it:

1. Explicit mentions: If the product name or description explicitly mentions the recording technology, I use that as the primary source of truth.

2. Model number identification: For certain specific model numbers known to use particular technologies, I apply the appropriate tag.

3. Brand, product line and capacity rules: For drives without explicit technology mentions, I apply tags based on established patterns from manufacturer documentation.

4. Cautious approach: Where I cannot determine with confidence which technology a drive uses, I leave it untagged rather than risk providing incorrect information.

Seagate Drive Classifications

For Seagate drives, I use the official Seagate documentation to apply tags based on:

• Product line (BarraCuda, IronWolf, etc.)
• Form factor (3.5” or 2.5”)
• Capacity

For example:

• 3.5” BarraCuda: 1TB models use CMR, while 2-8TB models use SMR
• All BarraCuda Pro drives use CMR
• 2.5” BarraCuda drives (500GB-3TB+) use SMR
• All IronWolf and IronWolf Pro drives (except 24TB HAMR models) use CMR

Western Digital Drive Classifications

Western Digital’s documentation is less consistent than Seagate’s, but I’ve developed rules based on their product documentation and community research:

• WD Red Plus and Red Pro: All models use CMR
• WD Red (standard): Current models (except 2.5” drives) use SMR, although some older models were CMR. Using the EFAX suffix to identify SMR drives I tag them as SMR, and use the EFRX suffix to identify CMR drives and tag them as CMR. If I can’t identify the model number I won’t tag the drive. We can collectively blame Western Digital for this mess.
• WD Gold, Purple, Purple Pro: All models use CMR
• WD Blue: Varies by model - 2.5” drives typically use SMR; 3.5” 8TB models use CMR - if I’m unsure I don’t tag the drive.
• WD_BLACK: All desktop (3.5”) models use CMR
• Ultrastar DC HC620: All models use host-managed SMR (HM-SMR)
• Ultrastar DC HC550/560/570: All models use CMR (some with ePMR/EAMR technology)

Drives I Don’t Tag (Uncertain Classifications)

I prioritise accuracy over completeness, so some drives remain untagged when I cannot confidently determine their recording technology:

• Older drive models with limited documentation
• Drives with inconsistent information across sources
• Enterprise drives with specialised configurations
• Certain Western Digital models:
  • WD Black 2.5” (various technologies based on capacity)
  • WD Blue 3.5” smaller than 2TB
  • Some Ultrastar models without clear documentation (DC HC510, HC520)
  • Models with conflicting information in different sources

Why This Matters to You

The choice between CMR and SMR has real-world performance implications:

• For NAS systems: CMR drives are generally recommended
• For backup or archival storage: SMR drives may offer better value
• For RAID arrays: CMR drives provide more consistent performance
• For general-purpose desktop use: Either technology can work well, depending on specific usage patterns but I’d recommend CMR for most users.

By tagging drives with their recording technology, PricePerGig.com helps you filter and find the right drive technology for your specific needs, avoiding potential compatibility issues or performance problems down the line.

Technical Implementation Details

For those interested in the technical details, here’s how my tagging system works:

1. I first normalise drive brand names (e.g., “WD” becomes “Western Digital”)
2. I identify the product line from the product name (e.g., “BarraCuda Pro”, “WD Red Plus”)
3. I extract the form factor (2.5” or 3.5”) and capacity
4. I check for explicit technology mentions in the product name
5. I apply brand-specific rules based on product line, form factor, and capacity
6. I apply model number specific rules for certain drive models
7. I regularly update my rule set as new information becomes available

This multi-layered approach helps me provide the most accurate information possible while acknowledging the limitations of manufacturer documentation.

Western Digital Tagging Logic

For Western Digital drives, the tagging system follows these key rules:

• Checks model numbers first (e.g., EFAX suffix typically indicates SMR for WD Red drives)
• Applies product line rules (e.g., all WD Red Plus and Pro drives are CMR)
• Considers form factor and capacity combinations
• Uses special rules for Ultrastar enterprise drives

For example, a simplified decision flow might look like:

Resources and References

For those wanting to learn more about drive recording technologies, I recommend:

• Seagate’s official CMR/SMR list
• Western Digital’s recording technology guide