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What I found when I checked my M1 MacBook Air SSD

Is your new Mac eating your costly SSD? Reports suggest that some new M1 Macs are wearing out their SSDs at alarming rates. I had to see for myself.

It's not like I need an excuse to buy a new Mac, but since my M1 MacBook Air is only two months old, it would need to be a really good excuse. "My SSD is dying!" would do.

To follow up on last week's article on Mac SSD deterioration, I decided to see for myself what was happening on my machine. With the aid of a post from Macworld's Roman Loyola I loaded smartmontools.

TL:DR version of the process: load Xcode (Apple's IDE); then Homebrew (a popular package manager); and then smartmontools which reads the SMART (Self-Monitoring, Analysis, and Reporting Technology) built into most drive controllers for the last 15 years. Xcode is 12GB, so it takes a while. (Update: Alert reader Jdanek pointed out that savvy users can simply download 430MB of Command Line Tools, saving time and drive space.)

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Roman's piece includes cut-and-paste commands to install the gizmos. After modest hiccups -- restarted Terminal a couple of times -- everything worked as planned. That said, if you aren't OK with command line interfaces, this is not the project for you.

The bad news

The data on the usefulness of SSD SMART reporting is limited. SMART wasn't all that useful for hard drives -- SMART looks at media behavior, but many failures are caused by electronic components going pff-ff-ft with little warning -- and SSDs are ONLY electronic components.

The good news

SSD controller architects have done a great job making cheap flash work for storage. So great, in fact, that the major paper on the subject, from Prof. Bianca Schroeder and Google engineers, found that drive age -- not use -- correlated with drive failure. Write On!

What did Smartmontools show me?

This screenshot shows the SMART data dump, but what does it mean?


Smartmontools output from an M1 MacBook Air.

I've had my MacBook Air for two months and about 3TB of data has been written to the 256GB drive. Apple doesn't specify what kind of NAND flash they use, but I'd guess it's the lowest cost per bit they can get from major suppliers.

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Which means Quad Level Cell (QLC) V (vertical) NAND. QLC is generally spec'd for ≈ 1,000 writes. For a 256GB SSD that means, naively, 256TB of total writes. At my present usage that equates to about 173 months -- or 14 years -- of write life.

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Which is what I'd expect from a modern SSD.

The Take

Two weakly held conclusions:

  • The excessive write behavior on M1 Macs isn't universal, based on my sample size of 1.
  • Don't pay much attention to SSD lifetime specs. They're set to reduce vendor warranty cost risk, not estimate actual SSD life.

If it does turn out that there is a bug that caused some SSDs to experience a shortened life, I'd expect that -- after the usual outcry -- Apple would take care of it. For what they charge for storage, they'd better!

Comments welcome. 

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