Relying solely on Availability Domains (ADs) is a high-availability (HA) strategy, not a disaster recovery (DR) strategy for a regional outage. ADs are physically separate, fault-isolated data centers located within the same OCI region. While this design protects against the failure of a single AD, it offers no protection if the entire region becomes unavailable. A robust DR plan for a regional outage fundamentally requires using a second, geographically distinct OCI region to host redundant resources and replicated data.

A. Backup and restore is a valid DR pattern (e.g., Pilot Light, Cold Standby) recommended for workloads that can tolerate higher recovery time objectives (RTO).
C. Creating redundant application instances in multiple regions is a primary strategy for achieving low RTO/RPO in an active-passive or active-active DR configuration.
D. Cross-region replication for services like Block Volume, Object Storage, and Autonomous Database is a critical component for protecting data against a regional failure.

1. Oracle Cloud Infrastructure Documentation, "Regions and Availability Domains": "An availability domain is one or more data centers located within a region... Use multiple availability domains to ensure high availability... To protect your applications from a regional failure, you can create a disaster recovery solution by using cross-region features." This source directly contrasts the use of ADs for HA with the need for cross-region solutions for DR.

2. Oracle Cloud Infrastructure Documentation, "Disaster Recovery in the Cloud": Under the section "Disaster Recovery Topologies," the document states, "A region is a localized geographic area, and an availability domain is one or more data centers located within a region... A disaster recovery solution requires at least two regions." This explicitly states that DR requires more than one region, making a single-region, multi-AD strategy insufficient.

3. Oracle Cloud Infrastructure Documentation, "Best practices for your cloud topology": In the section "Plan for disaster recovery," it advises, "To ensure that your solution is resilient to the failure of an entire region, we recommend that you deploy in multiple regions... Don't rely on backups in the same region." This reinforces that single-region strategies, including those relying only on ADs, are not sufficient for DR.