114 lines
6.2 KiB
Markdown
114 lines
6.2 KiB
Markdown
# Fenris
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Fenris observes an NVMe drive’s real-world use and translates that history into an understandable endurance outlook.
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## Language
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**Observation history**:
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The persisted record of drive activity gathered while Fenris monitoring is enabled, retained across restarts and reboots.
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_Avoid_: Calibration data, temporary history
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**Observed usage habit**:
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The pattern of active, idle, and powered-off hours represented by the observation history, with recent sustained behavior carrying more relevance than distant behavior.
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_Avoid_: Current usage, benchmark workload
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**Usage-adjusted theoretical lifespan**:
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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.
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_Avoid_: Future life, actual lifespan, failure date
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**Projection confidence**:
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The degree to which the observation history is sufficiently long, complete, and stable to support the usage-adjusted theoretical lifespan.
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_Avoid_: Accuracy percentage, certainty
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**Monitoring period**:
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A span during which Fenris monitoring is enabled; powered-off time remains part of the usage habit, while deliberately disabled time does not.
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_Avoid_: Daemon uptime, calibration window
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**Observation store**:
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The single SQLite database at `/var/lib/fenris/observations.db` that persists the observation history, monitoring periods, hour observations, day aggregates, and endurance baseline.
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_Avoid_: Data directory, history.jsonl, the database (generic)
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**Store fault**:
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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.
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_Avoid_: Database error, corruption, broken data
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**Usage interval**:
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The elapsed span between two compatible counter observations, with a measured usage total whose distribution within that span may be unknown.
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_Avoid_: Estimated hourly usage, interpolated sample
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**Unallocated usage**:
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Measured usage whose share in a particular hour, calendar day, or monitoring period cannot be established from the available evidence.
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_Avoid_: Zero usage, evenly distributed writes
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**Hour observation**:
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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.
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_Avoid_: Hourly record, hourly.jsonl entry
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**Day aggregate**:
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The UTC-day summary at which usage-habit evidence is judged; distinct from a local display day.
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_Avoid_: Local daily total, daily stats
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**Local display day**:
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A calendar day in the user's current system timezone, used to browse observation history; its elapsed length can vary with timezone transitions.
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_Avoid_: UTC evidence day, fixed 24-hour day
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**Controller segment**:
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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.
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_Avoid_: Counter reset handling, drive swap detection
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**Degraded identity**:
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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.
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_Avoid_: Identity error, unknown device, virtual drive
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**Endurance baseline**:
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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.
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_Avoid_: TBW value, failure threshold, max writes
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**Verified override**:
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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.
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_Avoid_: Confirmed TBW, trusted value
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**Unverified override**:
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A rated-TBW override knowingly stored with incomplete provenance; always presented as user-supplied, never as verified.
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_Avoid_: Forced entry, fallback baseline
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**Sustained regime**:
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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.
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_Avoid_: Current window, detection period
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**Habit change**:
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A sustained divergence between recent and earlier daily write rates that starts a new sustained regime.
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_Avoid_: Spike, anomaly
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**Scenario range**:
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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.
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_Avoid_: Confidence interval, error bar
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**Coverage**:
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The share of wall-clock seconds inside monitoring periods whose usage-habit classification is known rather than unknown.
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_Avoid_: Uptime, sample count
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**Byte-allocation completeness**:
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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.
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_Avoid_: Coverage, estimated allocation
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**Qualifying day**:
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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.
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_Avoid_: Completed day, supported day, calibration day
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**Collection run**:
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One scheduled or on-demand execution of the collector that interrogates the drive and extends the observation history.
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_Avoid_: Poll, daemon tick
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**Release**:
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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.
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_Avoid_: Tag, upload, build
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**Rollback**:
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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.
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_Avoid_: Downgrade, version pinning (as a promise)
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**Deliberate disable**:
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A monitoring pause made through Fenris's own control path, closing the monitoring period so the paused time is excluded from the usage habit.
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_Avoid_: Manual stop, service stop
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