All-In-One usually means high iops = fast 2,5" 10k rpm disks or better 2,5" SSD only storage
Why not using a ready to use SuperMicro system with 10G Ethernet and 3 x 12G HBA in IT mode:
Supermicro | Products | SuperServers | 2U | 2028R-ACR24L
You only need to select CPU and RAM.
Such a system is perfect for software raid like ZFS