# Fenris

Fenris observes an NVMe drive’s real-world use and translates that history into an understandable endurance outlook.

## Language

**Observation history**:
The persisted record of drive activity gathered while Fenris monitoring is enabled, retained across restarts and reboots.
_Avoid_: Calibration data, temporary history

**Observed usage habit**:
The pattern of active, idle, and powered-off hours represented by the observation history, with recent sustained behavior carrying more relevance than distant behavior.
_Avoid_: Current usage, benchmark workload

**Usage-adjusted theoretical lifespan**:
The theoretical time until the drive’s write endurance is exhausted if its observed usage habit continues; it is an endurance projection, not a predicted hardware-failure date.
_Avoid_: Future life, actual lifespan, failure date

**Projection confidence**:
The degree to which the observation history is sufficiently long, complete, and stable to support the usage-adjusted theoretical lifespan.
_Avoid_: Accuracy percentage, certainty

**Monitoring period**:
A span during which Fenris monitoring is enabled; powered-off time remains part of the usage habit, while deliberately disabled time does not.
_Avoid_: Daemon uptime, calibration window

**Observation store**:
The single SQLite database at `/var/lib/fenris/observations.db` that persists the observation history, monitoring periods, hour observations, day aggregates, and endurance baseline.
_Avoid_: Data directory, history.jsonl, the database (generic)

**Store fault**:
The condition where the observation store is present but cannot be read or trusted — unreadable, corrupt, or written by a newer Fenris — degrading every view that depends on it rather than crashing or guessing.
_Avoid_: Database error, corruption, broken data

**Usage interval**:
The elapsed span between two compatible counter observations, with a measured usage total whose distribution within that span may be unknown.
_Avoid_: Estimated hourly usage, interpolated sample

**Unallocated usage**:
Measured usage whose share in a particular hour, calendar day, or monitoring period cannot be established from the available evidence.
_Avoid_: Zero usage, evenly distributed writes

**Hour observation**:
The usage-habit evidence for a UTC hour's represented elapsed span: active, idle, powered-off, and unknown time, measured usage, thermal evidence, and coverage. A partial hour does not describe future time.
_Avoid_: Hourly record, hourly.jsonl entry

**Day aggregate**:
The UTC-day summary at which usage-habit evidence is judged; distinct from a local display day.
_Avoid_: Local daily total, daily stats

**Local display day**:
A calendar day in the user's current system timezone, used to browse observation history; its elapsed length can vary with timezone transitions.
_Avoid_: UTC evidence day, fixed 24-hour day

**Controller segment**:
A span of observation history within which the drive's controller identity is unchanged and counters are monotonic; write deltas are never computed across a segment boundary.
_Avoid_: Counter reset handling, drive swap detection

**Degraded identity**:
The condition where a controller segment's identity key is blank because no identifier rung produced a value; replacement detection then relies on write-counter continuity alone, and projection confidence is capped.
_Avoid_: Identity error, unknown device, virtual drive

**Endurance baseline**:
The write-endurance value a projection consumes, chosen by precedence: a verified override when one exists, otherwise an unverified override, otherwise a coarse implied baseline derived from vendor wear — each labeled as such.
_Avoid_: TBW value, failure threshold, max writes

**Verified override**:
A rated-TBW override with complete provenance whose applicability to the detected drive was confirmed by machine match or explicit user attestation; the strongest endurance baseline.
_Avoid_: Confirmed TBW, trusted value

**Unverified override**:
A rated-TBW override knowingly stored with incomplete provenance; always presented as user-supplied, never as verified.
_Avoid_: Forced entry, fallback baseline

**Sustained regime**:
The most recent stretch of the observation history over which the observed usage habit has been stable; the interval whose write rate the usage-adjusted theoretical lifespan consumes.
_Avoid_: Current window, detection period

**Habit change**:
A sustained divergence between recent and earlier daily write rates that starts a new sustained regime.
_Avoid_: Spike, anomaly

**Scenario range**:
The spread of lifespan projections computed from the 7-, 28-, and 90-day horizons of the observation history, shown in place of a statistical interval.
_Avoid_: Confidence interval, error bar

**Coverage**:
The share of wall-clock seconds inside monitoring periods whose usage-habit classification is known rather than unknown.
_Avoid_: Uptime, sample count

**Byte-allocation completeness**:
Whether the available evidence establishes all monitored writes attributable to a specified span, without missing counter evidence or unknown boundary shares; distinct from usage-habit classification coverage.
_Avoid_: Coverage, estimated allocation

**Qualifying day**:
A UTC date whose represented monitored time meets the coverage requirement for projection evidence. Qualification is provisional while the date is in progress and does not establish byte-allocation completeness.
_Avoid_: Completed day, supported day, calibration day

**Collection run**:
One scheduled or on-demand execution of the collector that interrogates the drive and extends the observation history.
_Avoid_: Poll, daemon tick

**Release**:
A published version of Fenris: a version tag, its packages in the channel, and its human-readable change notes, all together; a bare tag is not one.
_Avoid_: Tag, upload, build

**Rollback**:
Returning to an earlier release by restoring an observation-store snapshot and then installing that release; installing an older package over a newer store is unsupported.
_Avoid_: Downgrade, version pinning (as a promise)

**Deliberate disable**:
A monitoring pause made through Fenris's own control path, closing the monitoring period so the paused time is excluded from the usage habit.
_Avoid_: Manual stop, service stop