Storage Spaces Direct (S2D)
Microsoft's software-defined storage: 2 to 16 servers pool their local NVMe and SSD drives into one highly available storage pool.
Storage Spaces Direct (S2D) in practice
Storage Spaces Direct (S2D) pools the local drives of 2 to 16 servers into a single software-defined storage pool — no SAN, no Fibre Channel, connected over ordinary Ethernet. Microsoft states an upper limit of more than 400 drives and 4 petabytes per cluster. On Windows Server, an all-flash deployment needs at least four capacity drives of the same type (NVMe or SSD) per server; if the storage pool cache is used, two cache drives per server are added on top.
10 GbE or faster with RDMA is recommended, because storage traffic between nodes runs over SMB Direct. A three-way mirror survives two simultaneous failures of drives or entire nodes. S2D ships in the Datacenter editions of Windows Server and is also the storage layer beneath hyperconverged Azure Local instances. Two deployment modes exist: hyperconverged, with Hyper-V and storage on the same nodes, or converged via a Scale-Out File Server. Alendris built an S2D cluster with NVMe storage and a 10G backbone for a manufacturing company.