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The difference between CMR and SMR hard drives and why it matters


I just ordered a new-old-stock CMR hard drive, and for good reason.

This year was supposed to be the one where I moved away from all computer storage media that physically moves, which means no more optical discs and no more hard disk drives.

I was able to get away from the discs; that wasn't a problem. As for hard disk drives, I found out the hard way that yes, still necessary, but for a very specific reason.

Before I get into that, let's talk about CMR and SMR. Those are not brands but rather abbreviations. CMR is Conventional Magnetic Recording and SMR is Shingled Magnetic Recording. CMR is the older tech.

The advantage to SMR is you get more space out of the drive. The disadvantage is that for big file writes to the SMR drive, the write speed can slow down. A lot. For file reads, yeah, SMR is fine for that. If I were using one for, say, playing back movies or some such, sure, no problem. But as a backup drive, I won't touch it, hence the reason I decided to go with the older CMR...

...which is not exactly easy to come by in 2.5" form factor. What I wanted was a 1TB HGST brand drive (small, I know, but it's all I need), and I had to order the stupid thing from overseas just to get it. At the time I write this, it's on the way here. Why HGST? I have a 500GB HGST I bought new years ago, it's still working a-okay and I'm hoping to get a repeat of that performance in 1TB flavor.

In the 3.5" size, the go-to hard drive for CMR is the Seagate Barracuda Pro. All of them are CMR, start at 2TB and blast up to 10TB and well beyond that for storage capacity. It's the tried-and-true good ol' 7200 RPM CMR hard disk drive. If you need something enterprise grade, then you step up to the Seagate Ironwolf, which are also all CMR (but probably also loud since they're meant for industrial use). The Seagate Skyhawk, meant for surveillance use, is CMR and notably quieter, but that's 5400 RPM and not 7200. The Skyhawk would probably make for a fine backup drive.

The Barracuda Pro would still be my pick if I were going the 3.5" size route. Grab one of those, install it in a box or an enclosure and you're good to go.

I said I discovered the hard way that HDD is still necessary.

What I found out is that using SSD for storing backup data is a bad idea. More specifically, nightly backups.

Writing a large amount of data to SSD sometimes is okay. The same can be said for any flash memory. If you have 5GB or more that you write to the media periodically, that's fine. If however this is done daily, that's when problems can happen with flash memory.

I didn't lose any data when I attempted to use SSD for nightly backups, but wow did the write speed dive. It was bad. With my aging 500GB HGST HDD, read and write speeds were (and still are) always consistent and speedy. No problems. With SSD, not only did write speeds dive but also fluctuated. Not wildly, but enough to raise my eyebrow and think, that really doesn't look right.

SSD as a host drive for the operating system? That's fine. Windows, Linux, whatever. It works. SSD for movies and music used write-once-read-many style? Again, fine. SSD for backup use? Not-so good from what I saw.

Why did I decide to use a 2.5" HDD? I already have drive enclosures for that size and I prefer the smaller form factor. But it's probably true what I just bought will be the very last CMR 2.5" HDD I ever own. After this, if I want to stick with a CMR HDD for a backup drive (and I do), I'll have to go with the larger 3.5".

For my host drive, that's staying as SSD. Absolutely. For my backup drive, that's staying as HDD with CMR. I thought SSD-for-everything would work, but HDD with CMR appears to still be the best thing for backup use, short of a NAS (more specifically, NAS with CMR HDDs in it).

Published 2023 Feb 16

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