> ## Documentation Index
> Fetch the complete documentation index at: https://docs.onebucket.io/llms.txt
> Use this file to discover all available pages before exploring further.

# Write once, land in several clouds

> One policy, several independent copies, one set of application keys

## The situation

Critical data needs a second copy outside the primary cloud: for resilience, for negotiating leverage with a provider, or because a regulator asks for it. Today that is a sync job per bucket, a second set of keys in every application, and a failover plan nobody has tested.

## What OneBucket changes

One policy maps the bucket to several peer buckets, each synchronous or asynchronous, with a write quorum you set. Applications write once and the copies land. A new provider joins by adding a peer bucket, and opportunistic replication fills it from existing data as it is read.

![One write through OneBucket lands on AWS S3, Wasabi and on-prem peers according to the replication policy](https://mintcdn.com/onebucket/IRmZGtHTOOl3yo0n/images/scenarios/replication.png?fit=max\&auto=format\&n=IRmZGtHTOOl3yo0n\&q=85\&s=8c18d5d38a4d341e65e40b038194cab8)

## How it works

* **Peer buckets.** A policy maps one OneBucket to one or more peer buckets at your endpoints. Each peer is in `sync`, `async` or `cache` mode.
* **Write quorum.** The quorum says how many write-enabled peers must succeed before the write is acknowledged. That is the dial between durability and latency, set per bucket.
* **Opportunistic replication.** When a peer is added, existing objects are copied into it as they are read, so a second provider is usable with its existing data right away rather than after a bulk copy. The asynchronous `flux` path fills the rest in the background.
* **Exit option.** Leaving a provider is a policy change, not a migration program: remove the peer, and the remaining copies carry on.

## Related

* [Set up your OneBucket](https://docs.onebucket.io/setup.md)
* [Placement by policy](https://docs.onebucket.io/scenarios/placement.md) when the copies must sit in specific jurisdictions
* [Migrate behind a fixed endpoint](https://docs.onebucket.io/scenarios/migration.md)


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