CMR vs SMR: Which Recording Technology Should You Buy?

If you’ve spent any time on storage forums, you’ve seen the CMR vs SMR debate. It gets heated. People act like SMR drives killed their dog. The truth is more nuanced — but the short version is: for most NAS and RAID users, CMR is the right choice. For single-drive backup and archival, SMR is fine.

Let me explain both, and then I’ll tell you exactly when each makes sense.

What’s the Difference?

CMR (Conventional Magnetic Recording)

CMR writes data in non-overlapping parallel tracks on the disk platter. Each track is independent — you can rewrite one track without touching its neighbors. This is how hard drives have worked for decades.

Key traits:

Consistent write performance
No performance degradation during random writes
Works great in RAID and NAS arrays
Handles multi-stream workloads well

SMR (Shingled Magnetic Recording)

SMR overlaps tracks like roof shingles — each new track partially overlaps the previous one. This lets manufacturers squeeze more tracks onto a platter, increasing density (and capacity) without increasing platter count.

The catch: when you need to rewrite data in the middle of a shingled zone, the drive has to rewrite the entire zone — not just the one track. This means:

Key traits:

Higher capacity per platter = cheaper per TB
Excellent sequential read/write performance
Terrible random write performance under sustained load
Can cause serious issues in RAID rebuilds

The NAS/RAID Problem

Here’s where it gets real. If you’re running a multi-drive NAS — TrueNAS, Unraid, Synology, whatever — your array does a lot of random writes. Parity calculations, metadata updates, snapshots, file system operations. SMR drives handle this poorly.

During a RAID rebuild (when a drive fails and you’re replacing it), the array does massive sustained writes to the new drive while simultaneously reading from all other drives. SMR drives can slow to a crawl during this process, and in some cases the rebuild takes so long that another drive fails before it completes. That’s a data loss scenario.

I’ve personally experienced this. Years ago I made the mistake of building a RAID-Z2 array with Seagate Archive drives (SMR). First rebuild took 4 days. A CMR array of the same size rebuilds in under 24 hours.

Bottom line: if you’re buying drives for a NAS or any RAID configuration, buy CMR. Check the best NAS drives page — everything listed there is CMR.

When SMR Is Totally Fine

SMR gets a bad rap, but it’s genuinely good for certain use cases:

1. Single-Drive Backup

If you’re plugging in an external drive, running a backup, and unplugging it, SMR is fine. You’re doing sequential writes — exactly what SMR handles well. And you often get more capacity per dollar.

2. Cold Storage / Archival

Write once, read occasionally? SMR excels here. The higher density means lower cost per TB, which is exactly what you want for data you’re storing long-term. Check the external drive deals for affordable archival options.

3. Media Streaming (Read-Heavy)

If the drive is primarily reading — serving Plex streams, for example — and you’re doing bulk writes only when adding new content, SMR works fine. The writes happen infrequently enough that the performance hit doesn’t matter.

4. Desktop/Laptop Secondary Storage

Games, photos, documents — a secondary drive that stores big files and doesn’t see constant small writes. SMR’s cost advantage makes it a good fit.

How to Tell If a Drive Is CMR or SMR

This is annoyingly harder than it should be. Manufacturers don’t always make it obvious. Here’s how to check:

Check the spec sheet: Look for “Recording Technology” in the technical specs. CMR is sometimes listed as “PMR” (Perpendicular Magnetic Recording) — same thing.
Check the model number: For Seagate, the Exos and IronWolf Pro lines are CMR. The Barracuda Compute line in 2TB+ is often SMR. For WD, Red Plus and Ultrastar are CMR. WD Red (non-Plus) in some capacities was SMR (this caused a whole controversy in 2020).
Check HDDHunt: I list the recording technology for drives where the data is available. On the CMR vs SMR comparison page, you can see current prices for both types side by side.

Price Comparison

Generally, SMR drives cost 10-20% less per TB than equivalent CMR drives. Whether that savings is worth it depends entirely on your use case:

Use Case	Recommendation	Why
NAS / RAID array	CMR only	Random write performance, rebuild safety
Single external backup	SMR is fine	Sequential writes, cost savings
Cold storage / archival	SMR is fine	Write-once workload, max capacity
Plex / media server (single drive)	Either works	Mostly reads, occasional bulk writes
Enterprise / data center	CMR only	Workload ratings, predictable performance

For current CMR drive prices, check the enterprise HDD page — enterprise drives are universally CMR and often competitively priced.

My Recommendation

If you’re reading this blog, you’re probably a data hoarder or home server enthusiast. Buy CMR for your array, buy whatever’s cheapest per TB for your offline backups. That’s been my strategy for years and it’s never let me down.

The specific drives I’d look at right now:

NAS duty: Seagate Exos X16/X18 or WD Ultrastar DC HC550 in 14-18TB — check current NAS drive pricing
Backup duty: Whatever hits the lowest price per TB in the deals page, CMR or SMR doesn’t matter for sequential backups
Need it all explained? The HDD buying guide breaks down what to prioritize

Don’t overthink it. CMR for multi-drive, SMR-okay for single-drive. That’s the rule.

Jake