Environmental service modules (ESMs)
A storage enclosure has two redundant ESM units, which can be hot-swapped. The ESMs are at the back of the enclosure. The ESM in SBB A is called ESM A, while the ESM in SBB B is called ESM B. One ESM continues to operate if the other ESM fails.
Note: To preserve the optimal airflow, do not remove a
failed ESM FRU from the chassis
until you are ready to replace it with a new FRU.
The ESMs contain the enclosure control logic, interface ports, and LEDs. Each ESM has two 6 Gbps x4 SAS In ports and a single 6 Gbps x4 SAS Out port. The SAS In ports are used to connect the ESM to a another ESM. The SAS Out port is used to cascade that ESM to another enclosure. The use of both ports on each ESM results in a redundant drive connection.
Figure 1 shows the location of the SAS In and SAS Out ports on the ESMs.
Figure 1. ESM SAS port locations