tail-hour · research · also tail hour

RAID tail hour

In The Tail at Store, a RAID tail hour is a group-hour in which at least one data drive has an hourly average I/O latency at least twice its group's median.

The event is defined at hourly resolution and does not measure the fraction of individual slow requests or establish simultaneous stalls. A relative baseline can miss a shared absolute slowdown. [1] The sample boundary differs from Perseus's workload-dependent slowdown ratio.

Relations

related

tail-latency, slowdown-ratio, fail-slow

Citations

1. Hao et al., The Tail at Store, FAST 2016, sections 3.3 and 6 (accessed 2026-10-15)
2. Hesela: Slow RAID hours are not request tail latency; source audit and reproducible counterexamples (accessed 2026-10-15)

JSON: /data/terms/tail-hour.json