How to check your Mac's SSD health

The built-in check (limited)

diskutil info disk0 | grep -i smart

   SMART Status:              Verified

Verified means the drive isn’t reporting a failure. Failing means back up now. That’s all macOS tells you; it says nothing about wear. You’ll see the same status in System Information › NVMExpress.

The real numbers: smartctl

Install smartmontools with Homebrew:

brew install smartmontools
smartctl -a disk0

disk0 is the internal SSD on Apple Silicon. If you get a permissions error, run it with sudo. The part you want:

SMART overall-health self-assessment test result: PASSED

SMART/Health Information (NVMe Log 0x02)
Critical Warning:                   0x00
Temperature:                        33 Celsius
Available Spare:                    100%
Available Spare Threshold:          99%
Percentage Used:                    2%
Data Units Read:                    123,456,789 [63.2 TB]
Data Units Written:                 98,765,432 [50.5 TB]
Power On Hours:                     4,812
Unsafe Shutdowns:                   37
Media and Data Integrity Errors:    0
Error Information Log Entries:      0

What each line means

Field	Meaning	Worry if
Percentage Used	The drive’s own estimate of rated endurance used	It’s approaching 100%
Data Units Written	Total written to the drive. The bracketed TB value is the readable one	It’s growing much faster than you’d expect
Available Spare	Reserve blocks left to replace worn ones	It drops toward the threshold
Available Spare Threshold	The level the drive considers critical	Spare is at or below it
Media and Data Integrity Errors	Uncorrectable errors	Anything above 0
Critical Warning	Any bit set signals a problem	Anything other than 0x00
Unsafe Shutdowns	Power cuts and forced shutdowns	Not a health measure; often dozens

Each “data unit” is 512,000 bytes, which is why smartctl does the TB conversion for you.

Percentage Used can go past 100%. That doesn’t mean the drive dies at that moment; it means it has exceeded its rated endurance and is more likely to wear out. Some people have also questioned how accurately early M1 drives reported this field, so treat it alongside the written total, not alone.

How much is a lot?

Apple doesn’t publish write endurance for its SSDs. Consumer NVMe drives are commonly rated in the hundreds of terabytes written, with larger capacities rated higher. So:

• Tens of TB after a few years: normal for a developer Mac.
• Over 100 TB in a year or two, on a 256 GB drive: a lot. Check why.

The useful number is your rate. Note Data Units Written today and again in a week:

smartctl -a disk0 | grep "Data Units Written"

At 50 GB a day, you write about 18 TB a year. Compare that against the drive’s age and Percentage Used, and you’ll have a fair idea how long it has left at your current pace.

Reduce writes if they’re high

• Memory pressure. Heavy swap is constant writing. If sysctl vm.swapusage shows many GB, see high swap usage on Mac.
• Docker. Rebuilding images, database volumes and logs write a lot. Prune what you don’t need (free up space on a developer Mac).
• Builds and installs. Fresh node_modules installs and Xcode builds write gigabytes. Reusing a package store (pnpm) and keeping DerivedData helps.
• Find the writer. Activity Monitor’s Disk tab, sorted by Bytes Written, shows the processes responsible since boot.

External drives

smartctl works on many external NVMe and SATA drives too, but USB enclosures often block SMART commands. Run diskutil list to find the disk number, then smartctl -a disk4. If it fails, the enclosure doesn’t pass the data through; Thunderbolt enclosures usually do better.

Keep a backup regardless

SSDs often fail without warning, and on an Apple Silicon Mac a dead internal SSD means a logic board repair. Health numbers help you plan, but Time Machine or another backup is what protects your data.

Doing this with Stat Space

Stat Space’s Disk tab reads the internal SSD’s NVMe health directly, without Homebrew or sudo: wear (percentage used), terabytes written, power-on time and errors. It sits next to per-volume usage, read and write speed, and the top apps by disk I/O, so you can see which process is doing the writing. The Disk tab is free.