Constant FSYNC_ERROR 

const FSYNC_ERROR: Duration;

p50 fsync latency above which the disk is logged as ERROR. Deliberately far above anything healthy, because there is no validated threshold yet: ordinary cloud block storage sits at 0.5-2ms and ZFS on an encrypted volume at ~3ms, so a lower bar flags working nodes. At half a second per commit a single durable write already costs a quarter of a ~2s view. Everything below this is reported as a number and left to the operator.