Failure signals
Signs of hard drive failure before SMART screams
SMART is a lagging dashboard; human senses and OS friction often fire earlier.
Filesystem hesitation
Explorer or Finder stalls on tiny metadata ops while CPU idles — sometimes IRPs pile up waiting on retries the disk hides until timeouts surface.
Latency tails under tiny IO
Micro-stutters during low-QD workloads differ from burst-heavy tasks. Graph latency separately if your tooling exposes it; Sentinel pairs well with noting SMART runtime increases.
Acoustic shifts
Seek chatter increasing while workloads stay flat suggests mechanical wear or head instability — treat as urgent even if realloc stays zero briefly.
What to do next
Image critical partitions first; verify backup restores on another machine. Replace proactively — degraded disks fail unpredictably during resilvers.