SAS-3 12Gb/s expander (Microchip/PMC 82885T), backward compatible with 6Gb/s; fans out more drives from one HBA/RAID.
I/O layout: 7× SFF-8643 internal + 2× SFF-8644 external; supports multiple uplinks for higher aggregate bandwidth.
Works with SAS natively; SATA via STP; RAID/JBOD decided by the upstream HBA/RAID controller.
Enclosure mgmt: SES-2/SGPIO for slot LEDs/status and thermal/fan signals with enterprise backplanes.
Easy deployment: PCIe edge for power only (or 4-pin); data over mini-SAS HD cables; widely used with TrueNAS, unRAID, Proxmox, ESXi.