The Silicon Image SIL3726 is a surface mounted device that provides the SATA port expansion function used in storage servers. Each SATA input can support 5 hard disks. By using such backplanes it’s possible to use a single disk controller card to manage all the disks in a server.


  • SATA II 3 Gb/s
  • SATA port multiplier compliant


  • 5 SATA II 3 Gb/s
  • Hot Plug support
  • NCQ support
  • SATA port multiplier compliant
  • 2 status LED per port

The chip is packaged in a 364 pin BGA. This works well modern layered logic board designs. The SIL3726 also has the capability to have the EEPROM upgraded however generally this is not needed once the prototype stage is completed.

The SIL3726 contains a SATA Enclosure Management Bridge (SEMB) to pass in-band enclosure management information between the host and an enclosure management device. This makes it easy for servers to identify which disk needs to be replaced etc.

Backblaze is using this chip with their storage servers which makes sense. The low cost of port expanders is what makes storage servers so much less expensive. Backblaze uses custom hardware while we like EIA 19″ racks which are standard.

SIL3726 block diagram