What is it and why is it important?
All hard drive manufacturers were caught some time ago using SMR technology in hard drives without disclosing it. This caused quite a stir, and since then it has become more obvious which technology a hard drive uses.
But let’s start at the beginning:
What exactly is CMR or SMR?
CMR (Conventional Magnetic Recording)
The classic method, which has been the standard for many years. Here, data tracks do NOT overlap, which ensures consistently high performance when reading and, above all, writing data.
The following sub-technologies fall into this category (non-overlapping data tracks):
- LMR (Longitudinal Magnetic Recording)
Older technology, less efficient layout. Replaced by PMR.
- PMR (Perpendicular Magnetic Recording)
The de facto standard for hard drives for a long time.
- CMR (Conventional Magnetic Recording)
Basically the same as “PMR”
- EAMR (Energy-Assisted Magnetic Recording)
Improved CMR, e.g. through:
-> HAMR (Heat-Assisted Magnetic Recording), Heat
-> MAMR (Microwave-Assisted Magnetic Recording), Microwaves
-> ePMR (Energy-Enhanced PMR), Energy
SMR (Shingled Magnetic Recording)
With this newer technology, which is considered critical, the data tracks overlap, which has some disadvantages. More on that in a moment. The technology is used to store even more data in the same space, thereby reducing costs. These subtypes of SMR exist:
- SMR (Shingled Magnetic Recording)
Overlapping data tracks. Their management differs and is divided into:
-> DM-SMR (Device-Managed SMR), the hard drive itself controls
-> HM-SMR (Host-Managed SMR), the host computer controls
-> HA-SMR (Host-Aware SMR), The host computer is “aware” that SMR is being used and behaves accordingly.
So what’s the problem?
There are several, here are the most important ones:
- SMR makes data recovery considerably more difficult.
- Completely unsuitable for RAID systems; even the smallest data changes require large sections to be rewritten, during which time the hard drive is virtually unavailable for other tasks.
- Write performance is significantly worse.
- Latencies are also noticeably worse.
Conclusion
When in doubt, only buy CMR hard drives—you can’t go wrong with those. Unfortunately, this isn’t as transparent as one would like it to be. Here you can see which hard drive sizes work with CMR technology: NAS Compares
With very few exceptions, ALL external 2.5″ hard drives over 1 TB (e.g., the WD_Black Game Drive with 5 TB capacity*) use SMR technology. Therefore, these can be excluded across the board.