---
title: "S3 Synchronous and Asynchronous Replication Intro"
slug: "s3-synchronous-and-asynchronous-replication-intro"
description: "Discover S3 sync and async replication setups for optimal data protection and disaster recovery in your environments."
updated: 2026-10-28T18:40:50Z
published: 2026-10-28T18:40:50Z
canonical: "docs.vastdata.com/s3-synchronous-and-asynchronous-replication-intro"
---

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

# S3 Synchronous and Asynchronous Replication Intro

> [!NOTE]
> ℹ️ Info
> 
> **Document purpose** This document outlines the key VAST Data replication configurations based on three dimensions: Replication mode (sync vs. async), user source (local vs. external provider), and permission model (bucket vs. identity policies). For each scenario, we provide a concise description, explain when and why it's relevant, and link to detailed configuration steps. The goal is to help users and field teams identify the right setup for each environment and accelerate deployment decisions.

## Introduction to VAST Data Replication

VAST Data replication provides robust data protection and disaster recovery by enabling the creation of replica copies of file systems, S3 buckets, and databases across remote clusters. Replication can be configured in **two modes** — **synchronous** or **asynchronous** — each tailored to different operational and resilience needs.

### Synchronous Replication

Synchronous replication ensures zero data loss (RPO = 0) by replicating every write operation immediately and atomically from the source cluster to the destination cluster. Only after the data is successfully written to both sides is an acknowledgment returned to the client. This mode is ideal for mission-critical workloads where consistency across sites must be guaranteed in real time. While the destination copy is always fully up to date, failover is a **manual** process — RPO is zero, but RTO is not, as service restoration time depends on operational procedures.

### Asynchronous Replication

Asynchronous replication captures the state of data at **scheduled points in time** using snapshots, and transfers only the changes since the last snapshot to one or more destination clusters. This approach supports **flexibility and scalability**, including **many-to-one** and **one-to-many** replication topologies, and is suitable for disaster recovery, long-term retention, and cross-region deployments. In the event of a failure, replicated data can be **failed over and resumed**, with a small risk of data loss limited to the replication interval.

## Synchronous vs. Asynchronous Comparison Table

> [!NOTE]
> ℹ️ Info
> 
> Use this comparison table to choose the type of replication solution that best fits your operational needs.

| **Feature** | **Synchronous Replication** | **Asynchronous Replication** |
| --- | --- | --- |
| **RPO (Recovery Point Objective)** | Zero (no data loss) | Greater than zero (depends on snapshot schedule) |
| **Write Behavior** | Writes are replicated instantly before acknowledgment | Writes are acknowledged immediately; replicated later |
| **Failover Readiness** | Immediate, with fully up-to-date data | Near-ready; may lose recent writes |
| **Latency Requirements** | Low latency, typically <10ms | Works over high-latency links |
| **Topology** | One-to-one per protected path; for different protected paths, they can be multi-directional with multiple clusters. | One-to-one, one-to-many, many-to-one. |
| **Use Case** | Mission-critical, zero data loss | Disaster recovery, long-term retention |
| **Write Access at Destination** | Read-write under normal operation (read-only only if the secondary loses connection to the primary). | Read-only until failover. |
| **Replication Frequency** | Continuous (real-time) | Scheduled or on-demand |

### Bucket Policy vs. Identity Policy Comparison Table

| **Feature** | **Bucket Policy** | **Identity Policy** |
| --- | --- | --- |
| **Scope of Application** | Specific to a **View (bucket)** | Applied to a **user or group**, affects access across **multiple views** |
| **Attachment** | Attached **only to a view** | Attached to **one or more users/groups** |
| **Replication Behavior** | **Replicated automatically** with the view | **Replicated manually**; must be **enabled and re-attached** to the remote local users/groups |
| **Lifecycle** | **Deleted automatically** when the view/bucket is deleted | Persists independently of the bucket lifecycle |
| **API Type** | Managed through **S3 API** | Managed through **VMS API** |
| **Best Use Case** | When access rules are **specific to a bucket/view** | When should rules follow a **user across** **many buckets/views** |
| **Multi-tenancy Suitability** | Suited for **view-based isolation** | Suited for **user-based identity control** |
| **External Identity Provider** | Not directly integrated | **No need to attach manually** if using external identity provider |

- [S3 Asynchronous Replication with Local Users and Identity Policy](/kb/docs/s3-asynchronous-replication-with-local-users-and-identity-policy)
- [S3 Asynchronous Replication with Local Users and Bucket Policy](/kb/docs/s3-asynchronous-replication-with-local-users-and-bucket-policy)
- [S3 Asynchronous Replication with Active-Directory Users and Identity Policy](/kb/docs/s3-asynchronous-replication-with-active-directory-users-and-identity-policy)
- [S3 Synchronous Replication with Active-Directory Users and Identity Policy](/kb/docs/s3-synchronous-replication-with-active-directory-users-and-identity-policy)
- [S3 Synchronous Replication with Active-Directory Users and Bucket Policy](/kb/docs/s3-synchronous-replication-with-active-directory-users-and-bucket-policy)