HBA
Host Bus Adapter — expansion card that connects host to storage devices. Common: SAS HBA (12 Gb/s), Fibre Channel HBA, NVMe HBA. Unlike RAID controller: HBA does no RAID, just exposes raw disks.
"IT mode" (Initiator-Target) on LSI/Broadcom cards = pure HBA. "IR mode" = hardware RAID. ZFS users require IT mode — RAID controller hides disk state and breaks ZFS checksum logic. Classic choice: LSI 9300-8i, 9400-16i. JBOD connection: 1 HBA + SAS expander → 48+ disks. Modern NVMe HBA: tri-mode (NVMe/SAS/SATA) PCIe cards for flex config. Cost: ~$200-500 typical.