Network traffic capture problem on AR750

[sfx2000]

Wonder if there’s a way to merge threads…

How to limit a LAN port bandwidth on AR750

Hello experts, I try to capture packets between 2 LAN ports on AR750 by tcpdump. As LAN ports are connected to hardware switch in SoC, I mirrored one LAN port to eth1. Packets can be captured, the problem is both TF card and USB disk writting speed is only 10MB, and LAN speed is about 11MB, so tcpdump dropped some packets. I wonder how to limit LAN port bandwidth to 8 or 9 MB/s ?