Durability Modes
Transit is deliberate about acknowledgement language.
It does not want "durable" to mean six different things depending on who is speaking.
Quick Reference
| Mode | What it means | What it does not mean |
|---|---|---|
memory | accepted in memory only; useful for tests and benchmarks | crash-safe durability |
local | durable on the local node under the shared-engine contract | remote-tier safety or cluster-wide confirmation |
replicated | the published handoff frontier exists for catch-up and promotion readiness | that every follower has applied the write |
quorum | a majority of configured cluster peers acknowledged before success | remote-tier durability |
tiered | the relevant immutable history is durable in the remote tier | that every node is caught up locally |
Local
local means the append is durable on the local node under the current shared-engine contract.
That is the hot-path durability boundary.
Replicated
replicated means the replicated handoff boundary is published.
That is the readiness boundary for failover. It means the immutable handoff unit exists for clustered restore/catch-up semantics and promotion checks; it does not automatically mean every follower has applied it or that later writes on the promoted node are already replicated.
Quorum
quorum means a majority of configured cluster peers have acknowledged receipt of the appended records before the write is considered durable.
This is the strongest distributed durability guarantee Transit offers. It requires a ClusterMembership provider so the engine can discover peers and calculate quorum size. If the required majority does not respond within the configured timeout, the append fails explicitly.
Tiered
tiered means the relevant immutable history is durable in the remote tier and can support cold restore independently of the primary's hot local head.
For the current local/filesystem runtime shape, transit storage probe is the command that verifies the effective configuration and reports the guarantee it can literally prove.
Why This Matters
These boundaries keep three bad habits out of the product:
- vague marketing claims
- server-only durability semantics
- confusion between publication, replication, quorum, and failover
When you read or write Transit docs, keep those four words separate. Each represents a distinct guarantee.
For the full failover model, read Failover.