Reading a SMART report without panic

SMART is the health reporting built into most hard drives and SSDs. On Linux, the smartctl tool from the smartmontools package prints it with a command such as smartctl -a /dev/sda, and many desktop disk utilities show a summary. The output is long, but only a few lines matter.

The overall verdict, usually PASSED, is the least informative part. Drives can pass and still be failing, because the threshold for a failed verdict is set conservatively by the manufacturer. Look instead at individual values. On SATA drives, the reallocated sector count, current pending sector count and offline uncorrectable count show areas that could not be read or written reliably. Any value above zero is worth noting; a number that keeps growing is a clear warning.

NVMe drives report differently. Watch the percentage used, which estimates how much of the rated endurance has been consumed, the available spare, and the media and data integrity errors. Temperature matters too: a drive that regularly runs hot will age faster.

A single odd reading is not a reason to panic. What counts is the trend, so save the output now and compare it in a month. If error counts rise, if the drive disappears from the system at random, or if files start to fail to read, treat the disk as unreliable.

The only real response to a worsening report is to make sure a recent backup exists and to plan a replacement. SMART can warn you in advance, but plenty of drives fail without any warning, which is the real reason to keep backups regardless of what the report says.