External drive support

macOS reads SMART from internal drives on its own. It cannot read it through most USB enclosures. This page explains why, and what to do about it.

Try the drive first. Thunderbolt and USB4 enclosures that present the drive as NVMe already work with no setup at all. Plug it in and check DriveChk before changing anything on your Mac.

Why USB drives are different

A USB enclosure presents the drive inside it as a generic disk. The health data is still on the drive — the enclosure simply has no route for the question, so macOS never asks. Bridging that gap needs a small kernel extension that passes the question through.

Once one is loaded, external drives answer exactly the same way internal ones do, and DriveChk reads them with no further setup.

What this costs you

Loading a kernel extension means lowering your Mac's boot security. That is a real reduction, it stays in effect until you turn it back, and it applies to the whole startup volume. It is reversible in the same place you set it.

DriveChk does not bundle a driver and cannot install one for you. That is deliberate: this should be a decision you make on purpose, not a step inside an installer. If you would rather not, everything else in DriveChk keeps working normally for your internal drives.

1. Allow third-party drivers

Find your Mac below. The steps genuinely differ, and the wrong ones send you looking for a setting that is not there.

Apple Silicon (M1 and later)›
  1. 1.Shut the Mac down completely.
  2. 2.Press and hold the power button until “Loading startup options” appears, then click Options and Continue.
  3. 3.Sign in as an administrator when asked.
  4. 4.From the menu bar choose Utilities → Startup Security Utility.
  5. 5.Select your startup disk, click Security Policy, and choose Reduced Security.
  6. 6.Tick “Allow user management of kernel extensions from identified developers”.
  7. 7.Click OK, authenticate, then restart normally.
Intel with a T2 chip (2018–2020)›
  1. 1.Restart and hold Command-R until the Apple logo appears.
  2. 2.From the menu bar choose Utilities → Startup Security Utility.
  3. 3.Authenticate with an administrator password when asked.
  4. 4.Under Secure Boot choose Medium Security or No Security.
  5. 5.Under Allowed Boot Media, allow booting from external media.
  6. 6.Restart normally.
Intel without a T2 chip›
  1. 1.Nothing to change. These Macs load signed third-party drivers under their normal security settings.

2. Install the driver

The established driver for this is the open-source SAT SMART driver, distributed by BinaryFruit. DriveChk detects it once it is installed and running — it does not ship it, and does not need to be told about it.

3. Approve it and restart

macOS blocks a newly installed kernel extension until you approve it by hand. Open System Settings → Privacy & Security, scroll to the bottom, click Allow beside the blocked software, then restart.

4. Check it worked

Plug in a USB drive and open DriveChk. Its setup guide re-checks continuously, so it will already know how far you got — you do not need to tell it anything. A drive that previously said no health data should now report its temperature, hours and wear.

If it still does not work

Some enclosures cannot pass SMART through at all — particularly cheap bridge chips and most RAID cabinets. No software fixes that; the drive is answering, the enclosure is not passing the question along.

Most USB flash drives also do not implement SMART, even when a pass-through driver makes them look as though they might. DriveChk says so plainly rather than pretending to read something that is not there. A surface scan still works on them, and on any drive — it reads every sector directly and does not depend on SMART at all.

Still stuck? Email me