You have recently upgraded a tape drive on a older switch to operate at 120MB/s from 80MB/s. Prior to purchasing the tape drives, you tested server dumps to a disk array across multiple ports and saw

Tape drives typically act as storage targets, not initiators, and this functional role would not inherently limit the data transfer rate to 100MB/s.

A 1 Gigabit Ethernet (1Gb/s) port has a theoretical maximum throughput of 125 MB/s, but real-world performance is typically capped around 90-110 MB/s due to protocol overhead. This aligns perfectly with the observed maximum speed of 100MB/s, indicating the 1Gb/s switch port is the bottleneck for the 120MB/s tape drive.

Buffer credits are primarily relevant for Fibre Channel flow control, and while important, their state would not typically impose a hard limit of exactly 100MB/s that is characteristic of a 1Gb/s Ethernet link.

While iSCSI utilizes Ethernet, the 100MB/s limit directly points to the physical 1Gb/s Ethernet link speed, regardless of the higher-level protocol used by the tape drive.