LEKUO SouthBridge Mini: How Fast Can 10 Ports Run?
One PCIe Gen4 x1 upstream link, ten downstream ports. Below, we break down the specifications, measured speeds, cable requirements, and how the 16Gbps upstream bandwidth is shared.
1. Card Overview
2. What Does 16Gbps Actually Mean?
- PCIe Gen4 x1 operates at 16 GT/s, with 128b/130b encoding, providing approximately 15.75 Gbit/s of effective bandwidth.
- Converted to file transfer rates: approximately 1.97 GB/s.
- Combined theoretical peak bandwidth of all ten ports: 2×10 + 3×5 + 2.5 + 4×6 = 61.5 Gbps.
- Upstream bandwidth as a proportion of the combined downstream peak: 16Gbps ÷ 61.5Gbps ≈ 26%.
If all ten ports are connected and running at full speed simultaneously, the 16Gbps upstream link cannot deliver the maximum theoretical speed to every port at once.
However, this card is designed to expand connectivity. In everyday use, USB ports are often connected to devices such as keyboards and mice, which typically consume little bandwidth. It is also uncommon for the network and SATA interfaces to reach full utilization simultaneously.
In typical usage scenarios, the upstream bandwidth is generally sufficient.
3. Two Type-C Ports
Measured Performance — CrystalDiskMark Sequential Read/Write
- The sequential read speed difference between normal and reversed connector orientations is approximately 1–2%, indicating normal MUX switching.
- A single port reaching 907 MB/s is equivalent to approximately 7.3 Gbps, consuming about 46% of the upstream bandwidth.
- If both Type-C ports run at full speed simultaneously, their combined throughput would reach approximately 14.5 Gbps, leaving the upstream link nearly fully utilized.
Cable Requirements: Use a cable rated for USB 3.2 Gen 2 (10Gbps). Many commercially available USB-C to USB-C cables support only USB 2.0 or 5Gbps. They may connect without any error message, but transfer speeds can drop by more than half.
4. Three USB-A Ports
Sequential read speeds across the three USB-A ports range from 421 to 426 MB/s. The approximate usable upper limit for a 5Gbps connection is 440 MB/s.
These three ports do not all originate from the same connection point. Identify the correct connection before installation.
5. One 2.5GbE Port
Cable Requirements: 2.5GBASE-T can operate at full speed over Cat5e cabling for distances up to 100 meters. Cat6a is not required.
This is one of the practical advantages of 2.5GbE over 10GbE: existing network cabling can remain in place.
6. Four SATA Ports
Measured Performance — All Four Drives Tested Simultaneously
- The practical performance ceiling for SATA 6Gbps is approximately 500 MB/s. All four drives are operating close to this level.
- Combined throughput across the four drives reaches approximately 1.85 GB/s, consuming about 94% of the upstream bandwidth.
When all four SATA drives operate simultaneously at high speed, the upstream link is nearly fully utilized.
7. All Nine Storage Ports Online Simultaneously
All nine storage devices were detected during simultaneous testing, with no drives disconnecting.
Individual port speeds decrease noticeably under this workload. This is not a fault; it is the result of the nine ports sharing the 16Gbps upstream bandwidth.
8. Temperature Under Full Load
The card uses fully passive cooling, with no fan.
9. Platform Compatibility
On a fnOS NAS, all nine drives connected through SATA and USB were recognized natively, without requiring additional drivers.
Conclusion
Ten ports. One 16Gbps upstream link.
The reason to choose LEKUO SouthBridge Mini is not simply the number of ports. It is the ability to add USB, networking, and SATA connectivity through a single PCIe x1 slot.
Before using it, consider which ports will operate at high speeds simultaneously. Understanding how the upstream bandwidth is shared helps set realistic performance expectations.
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