You have a single fabric with four servers connecting to an edge switch in a core edge configuration with single 2Gb/s ISLs to the core. Each server has an average throughput requirement of 40MB/s…

Even if a single ISL provides sufficient bandwidth for current throughput, adding a second ISL creates an alternative physical path between switches. This redundancy ensures that if the primary ISL fails, traffic can still flow between the edge and core switches, preventing a single point of failure and maintaining fabric connectivity.

With four servers requiring 40MB/s each, the total throughput is 160MB/s, which is well within the 250MB/s capacity of a single 2Gb/s ISL, so an additional ISL is not strictly needed to avoid congestion based on the stated average throughput.

FSPF (Fabric Shortest Path First) updates are network control traffic and do not typically require a dedicated ISL for separation; they share the data path and have minimal bandwidth impact.

ISLs are for data and control plane traffic between switches, not for providing a separate management path for network devices; management is typically handled via dedicated out-of-band networks or in-band IP interfaces.