Document journal-copy replacement and correct failure-domain sizing rules - #203
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Document journal-copy replacement and correct failure-domain sizing rules#203wmousa wants to merge 2 commits into
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… removal Failure-domain node removal already documented that failover-path relocation can require a cross-domain target and refuses the removal if none exists. It never documented the journal (JM) redundancy set's own replacement behavior, which runs at the same time but in the opposite direction: the control plane prefers a replacement from the departed node's own failure domain, to leave the set's domain distribution unchanged rather than reshuffled -- a best-effort preference, never a removal blocker. Adds a new "Journal Copy Replacement on Removal" section to the architecture concept page, and cross-references it from both the Kubernetes and non-Kubernetes "failure domain" operations pages, next to their existing failover-path relocation coverage. Verified with scripts/quality-gate.sh (spelling, terminology, american, prose, voice, punctuation, syntax) -- clean for all three files.
…zing table Two claims in the failure-domain docs no longer matched the code: - "At least parity chunks + 1 domains" for surviving a domain outage was the bare rotation-correctness floor, not the actual activation gate. Fresh activation now hard-requires parity chunks + 2 distinct domains (2 domains is never sufficient, at any parity-chunk count) so a later single add/remove always has a spare host to relocate onto, rather than stranding a failover path immediately. - "If no such node exists, the removal is refused" skipped a fallback: the control plane now splices a stranded failover path into an already-formed pairing (rebuilding that host's own path elsewhere) before actually refusing the removal. Replaces the old goal/recommendation table with a domain-count x erasure-coding-scheme sizing table showing exactly how much simultaneous node or domain loss each combination tolerates, derived from the same per-domain risk-budget formula the node-shutdown capacity check uses (chunks_per_domain = ceil((ndcs+npcs) / domains), capped contribution per domain, summed against a parity-chunks budget). Verified with scripts/quality-gate.sh (spelling, terminology, american, prose, voice, punctuation, syntax) -- clean for both files; the syntax gate's remaining failures are pre-existing broken CLI-reference links in unrelated, untouched files.
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Documents the journal-copy replacement behavior on failure-domain node removal,
and corrects two claims that no longer matched the code:
bare rotation-correctness floor, not the actual activation gate. Fresh
activation now hard-requires parity chunks + 2 distinct domains (2 domains
is never sufficient, at any parity-chunk count) so a later single add/remove
always has a spare host to relocate onto, rather than stranding a failover
path immediately.
control plane now splices a stranded failover path into an already-formed
pairing (rebuilding that host's own path elsewhere) before actually
refusing the removal.
Adds a "Journal Copy Replacement on Removal" section to the architecture
concept page (cross-referenced from both the Kubernetes and non-Kubernetes
operations pages), and replaces the old goal/recommendation table with a
domain-count x erasure-coding-scheme sizing table showing exactly how much
simultaneous node or domain loss each combination tolerates -- derived
directly from the same per-domain risk-budget formula the node-shutdown
capacity check uses (chunks_per_domain = ceil((ndcs+npcs) / domains), capped
contribution per domain, summed against a parity-chunks budget), not guessed.
Verified with scripts/quality-gate.sh (spelling, terminology, american,
prose, voice, punctuation, syntax) -- clean for all three touched files; the
syntax gate's remaining failures are pre-existing broken CLI-reference links
in unrelated, untouched files.