macOS: S.M.A.R.T. status checks

Recently I was off for a few days, and before leaving, I shut down the machines, including the Mac Mini server, which has an external disk.

When back, the disk refused to show up. I tried various resuscitation methods, including reformatting it; initially the disk appeared ok, but when I started restoring data on it, after a while it became very, very slow. I smelled trouble.

Being an external LaCie disk connected via FireWire, macOS is not able to run the S.M.A.R.T. checks on it.

The solution was to temporarily install the disk in a Synology DS server, and run the S.M.A.R.T. tests there. The result was unpleasant, but not surprising: 36 bad sectors.

I found a replacement disk, and ran a full S.M.A.R.T. test, also using the Synology; the new disk had no problems.

The TimeMachine daily backups helped restore the disk without problems.

But the real problem behind the story is not that the disk got bad blocks, given several years, sooner or later all disks will do so.

The problem is that in my setup I had no way of knowing when the first bad sector happened, to take corrective actions.

Interface and macOS limitation

The reason is the way the S.M.A.R.T. test was designed to run: via ATA or SATA. When the disk is connected via USB or FireWire, apparently there is no standard way of forwarding these commands; the macOS USB or FireWire drivers do not provide any support for S.M.A.R.T., and I doubt they’ll ever do.

The only possible solution for an external disk is to use eSATA; the Mac Mini does not have a physical eSATA port, but apparently the thunderbolt port is capable of providing an adapter to it.


There are two recommendations:

  • enable S.M.A.R.T. monitoring an all disks, configure it to run often (at least daily) and report on any error
  • on macOS, connect external disks via eSATA, to have access to S.M.A.R.T.

The Synology servers directly integrate the S.M.A.R.T. monitoring features into the system, and allow to periodically run the tests, either the brief or the full ones. I run the brief tests daily and the full tests weekly.

For macOS Sierra I could not identify any support for S.M.A.R.T. in the system; fortunately there are third party solutions, even free ones, like SMARTReporter.

For connecting eSATA disks, the solution is a Thunderbolt to eSATA adapter; for new machines, Thunderbolt support is available via the nice USB-C connector, and it is expected to remain a long lasting standard option. For older machines, with Thunderbolt 1 connectors, an (already obsolete) adapter must be used, for example the Kanex Thunderbolt 1 & 2 to eSATA & USB 3.0 Adapter, still available from Amazon.



About Liviu Ionescu (ilg)
Hi! My name is Liviu Ionescu (ilg, ilegeul or eunete for colleagues and friends) and I’m a senior IT engineer. Or should I say a real programmer?

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