Zero RPO. Two Sites. One Cluster.
Azure Stack HCI Stretched Cluster extends a single HCI cluster across two physical locations with synchronous Storage Replica replication — providing zero-RPO disaster recovery and automatic VM failover without dedicated DR infrastructure.
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Storage Replica (SR) replicates storage volumes synchronously between the two sites at the block level — every write is confirmed at both sites before acknowledging to the application. This delivers zero RPO: no data is lost even on complete site failure.
Windows Server Failover Clustering continuously monitors node and site health. On site failure, VMs are automatically restarted on the surviving site — typically within minutes. Storage is already up to date at the surviving site, eliminating manual recovery steps.
Both sites run production workloads simultaneously in an active-active or active-passive configuration. The same nodes that serve production traffic at Site A are the DR target for Site B — and vice versa. This eliminates the cost of idle DR hardware.
Sites can be separate buildings, floors, rooms, or data centres in different cities. Synchronous replication requires ≤5ms round-trip latency. Sites with higher latency can use asynchronous replication for non-zero RPO scenarios.
The stretched cluster appears as a single entity in the Azure portal and Windows Admin Center — one cluster, one billing entry, one management console spanning two physical locations. Storage Replica status and health are visible alongside standard cluster metrics.
A lightweight witness node or cloud witness (Azure Blob Storage) provides cluster quorum in split-brain scenarios — ensuring the surviving site can achieve quorum and restart VMs even if both sites momentarily lose connectivity to each other.
Azure Stack HCI Stretched Cluster provides enterprise-grade disaster recovery within a single HCI cluster spanning two physical sites. By combining Windows Server Failover Clustering (WSFC) with Storage Replica synchronous block replication, a stretched cluster delivers zero-RPO business continuity — no data loss on site failure — without the complexity and cost of traditional SAN-based replication or dedicated DR appliances.
The cluster requires an even number of nodes split equally between two sites, a minimum of four nodes total (two per site), and a network link between sites with ≤5ms round-trip latency for synchronous replication. When this latency requirement cannot be met, asynchronous replication is available at the cost of a non-zero RPO. A witness node or Azure cloud witness ensures quorum can be achieved by the surviving site independently, preventing split-brain scenarios from preventing VM restart.
From a management perspective, the stretched cluster is indistinguishable from a standard Azure Stack HCI cluster — it registers with Azure, appears in the Azure portal, and is managed through Windows Admin Center. The same Azure Stack HCI subscription pricing applies, and all standard features including Arc Resource Bridge, AKS, Azure Monitor, and Defender for Cloud are fully supported. The result is enterprise multi-site DR at HCI simplicity and cost.
Zero-RPO replication meets the data loss tolerance requirements of banking, trading, and insurance systems — regulatory frameworks including FCA SYSC and PRA PS6/21 demand minimised RTO/RPO for critical systems.
Hospital and healthcare EPR systems cannot lose patient data — synchronous replication across two on-premises sites provides GDPR-compliant data sovereignty with zero RPO that cloud-only approaches cannot offer.
Operational Technology and SCADA systems running on HCI can achieve site-level resilience — critical factory floor systems continue operating from Site B automatically if Site A suffers a power or network failure.
Organisations with two data centres can consolidate HCI workloads into a stretched cluster — eliminating standalone DR infrastructure while maintaining full site-level resilience at lower total cost.
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