The impact of the EPLD update of the supervisor module on the Cisco MDS 9000 switches is that the redundant supervisor takes over while the EPLD update is in progress and there is no service disruption. EPLD (Electronic Programmable Logic Device) is a firmware component that controls the functionality of various hardware modules on the switch, such as the supervisor, line cards, and fabric modules. The EPLD update is performed to enhance the performance and features of the hardware modules, and to fix any bugs or issues.
The EPLD update process requires a reload of the affected module, which can cause a temporary loss of connectivity and traffic. However, if the switch has a redundant supervisor module configured in high availability mode, the EPLD update can be performed without any service disruption. This is because the redundant supervisor takes over the control plane functions while the active supervisor is being updated, and then switches back to the active supervisor when the update is completed. The EPLD update does not affect the data plane traffic, as the line cards and fabric modules continue to forward packets during the update process. References :=
* Implementing and Operating Cisco Data Center Core Technologies (DCCOR) v1.2, Module 7: Data Center Storage Connectivity, Lesson 7.3: Fibre Channel Protocol
* Cisco MDS 9000 Family NX-OS System Management Configuration Guide, Chapter: Installing Software Images and EPLDs, Section: Updating EPLDs