Pivot3 Acuity supports a minimum of 3 X-series nodes when local High Availability (HA) is required. The minimum base configuration consists of 2 Flash Accelerator nodes + 1 non-accelerator node. Two Accelerator nodes are required, because the NMVe PCIe cards are used as write-buffer and all writes are mirrored between these two nodes.
Pivot3 Acuity also supports 1-node configurations when local HA is not required, eg. in ROBO deployments.