Motherboard SATA ports are often limited. An HBA (specifically SAS HBAs) can support dozens of drives using expander cables. They provide "direct access" to disks, which is critical for modern filesystems like ZFS. What to Look For:
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In the world of home servers (like Unraid or TrueNAS), an HBA is a PCIe card that allows you to connect more hard drives than your motherboard supports. Motherboard SATA ports are often limited