In the hard drive market, there are two main types of recording technologies used: CMR (conventional magnetic recording) and SMR (shingled magnetic recording). WD produces drives using both technologies, so it can be confusing to figure out which models specifically utilize CMR.
What is CMR?
CMR is the traditional recording technology that has been used in hard drives for decades. It writes tracks of data that are separated from each other, so any track can be overwritten without affecting adjacent tracks.
Key advantages of CMR drives:
- Faster write speeds – data can be written randomly without needing to rewrite adjacent tracks
- Better for operating systems and applications – more optimized for random access
- Higher rewrite cycle tolerance – individual tracks can be overwritten multiple times
What is SMR?
SMR is a newer recording technology that was introduced around 2013. It writes tracks of data that overlap partially with each other, similar to shingles on a roof.
Key characteristics of SMR drives:
- Allows for higher data density – more tracks are squeezed into the same space
- Sequential write performance is fast since new tracks extend existing ones
- Random writes are slower since adjacent tracks may need to be rewritten
- Not ideal for operating systems or applications requiring fast random access
Why do some WD drives use SMR?
WD and other manufacturers adopted SMR technology as a way to offer increased drive capacities at lower costs. For things like archives and backups that mainly need sequential access, SMR provides an advantage.
However, SMR’s downsides like slower random access make it less suitable for primary storage in things like desktop PCs. WD reserves CMR drives for products intended for boot drives and high-performance applications.
How to identify CMR vs SMR WD drives
WD does not explicitly indicate CMR vs SMR technology on most of its consumer drive labels or specifications. However, there are some general guidelines:
- WD Red NAS drives use CMR up to 10TB models, and SMR on higher capacities like 12TB+
- WD Blue 3.5″ desktop drives are CMR
- WD Green 2.5″ and 3.5″ drives are SMR
- WD Black 2.5″ and M.2 NVMe drives are CMR
- WD Purple surveillance drives use both CMR and SMR depending on capacity
Identifying CMR vs SMR in WD Red NAS drives
Determining CMR vs SMR on WD Red drives is trickier since they switched to SMR starting with 10TB+ models in 2018. Here are some guidelines:
| Drive Model Number | Capacity | Recording Technology |
| WD10EFRX | 1TB | CMR |
| WD20EFAX | 2TB | CMR |
| WD30EFRX | 3TB | CMR |
| WD40EFRX | 4TB | CMR |
| WD60EFRX | 6TB | CMR |
| WD80EFAX | 8TB | CMR |
| WD100EFAX | 10TB | CMR |
| WD120EMAZ | 12TB | SMR |
| WD140EFFX | 14TB | CMR |
In mid-2020, WD introduced new WD Red Plus drives that use CMR exclusively, while regular WD Red now uses both CMR and SMR depending on capacity. Check individual drive specs to confirm.
Identifying CMR vs SMR in WD Purple drives
WD Purple surveillance drives also use a mix of both CMR and SMR depending on capacity:
| Drive Model Number | Capacity | Recording Technology |
| WD10PURZ | 1TB | CMR |
| WD20PURZ | 2TB | CMR |
| WD30PURZ | 3TB | CMR |
| WD40PURZ | 4TB | CMR |
| WD60PURZ | 6TB | CMR |
| WD82PURZ | 8TB | SMR |
| WD121PURZ | 12TB | SMR |
| WD181PURZ | 18TB | SMR |
Should I avoid SMR drives?
SMR drives can still be a good choice depending on your usage. For things like:
- Archival storage
- Backups
- Media libraries
- IR security camera storage
The sequential write performance of SMR is fine and you get more storage density per dollar. Just don’t use SMR for booting operating systems or applications requiring heavy random access.
Conclusion
Identifying whether a WD drive uses CMR or SMR can be tricky, since the specifications generally don’t mention the recording technology. Your best bet is to lookup the specific drive model numbers and capacity to determine which type of recording it utilizes.
For NAS or primary storage, stick with WD Red Plus or lower capacity WD Red drives to ensure you get CMR. For secondary storage like archives, backups, and media libraries, SMR drives like WD Green can provide good value.
As long as you match the recording technology appropriately with your usage, both CMR and SMR WD drives can be a great choice.