Three shapes, three use cases
Block storage for virtual infrastructure, attached over Fibre Channel SAN or iSCSI. Continuous availability here comes from synchronous replication with automatic failover.
HCI or dHCI delivers storage, compute and networking from the same box. The main advantage is integrated management, and the price is that compute and capacity grow together.
Scale-out on software-defined storage for file services over CIFS and NFS, or for object storage. Data can sit across several sites, which is how very high availability figures are reached.
As a backup target, object storage adds the part that matters: S3 Object Lock protects what has been written from being changed, including when production credentials are already compromised. Spread across several sites, an architecture like that reaches data availability of up to 14 nines.
What actually decides it
Usually the recovery time and the number of sites involved, less often the capacity. We settle those two values at the start, because they determine the shape of the build.
All-flash with NVMe brings the latency down. It does nothing for availability; replication and failover do that.
Hybrid systems with flash and disk remain the right choice where capacity matters more than latency.
