You can find the part number using redfish   For redfish you can perform get on "/redfish/v1/Chassis/System.Embedded.1/Assembly" URI  
Is it possible to identify the part number for the RAID controller without opening the server? I have 2 x T640 servers that are running 24x7. Ideally, I would like to purchase a spare RAID controller "just in case". Is it possible to identify the part number of the RAID controller through IDRAC so that I can purchase the correct part? Or do I need to resort to opening one of the servers? Many thanks for any info.
Identify RAID controller without opening server T640