Synchronous replication is a high-performance disaster recovery solution designed to provide a Zero Recovery Point Objective (RPO) by mirroring every write operation in real-time between two clusters. Because the system must wait for the remote site to acknowledge every write before confirming the operation to the application, the underlying storage media must be capable of extremely low-latency I/O.

On hybrid clusters that utilize both Solid State Drives (SSDs) and Hard Disk Drives (HDDs), Nutanix mandates a minimum of one SSD per node to support synchronous replication. The SSD tier is used to store metadata and provide the high-speed " Oplog " where incoming writes are initially landed before being drained to the HDD tier. If a cluster were to attempt synchronous replication using only HDDs (Option D), the mechanical latency of the spinning disks combined with the network Round Trip Time (RTT) would cause severe application performance degradation, failing the business requirement. Even though the cluster has large capacity requirements (100 TB), the presence of an SSD tier is a technical prerequisite for the software to even enable the synchronous consistency feature. Therefore, ensuring at least one SSD exists in every node of the hybrid cluster is the critical storage validation step required before implementation.