Just sharing my experience or both X25-E & X25-M on the IMS.
That "Dongle" is basically doing 2 things:
1.Making sure that the SSDs are being recognized as SAS device so that the redundancy of the storage controller would work
2.Providing a more consistent performance at the I/O level
However, you will not benefit much from using X25-E as the LSI controller is just too slow. We are still wondering why Intel didn't want to include IOP348 in the IMS. Even with IOP348 (We are trying it with Adpatec 5805Z), it is very tough to make X25-M running at its potential as IOP348 is not really designed to support SSDs.
I seriously urge Intel to replace that slow LSI storage controller with IOP348, this was the reason we decided not to buy the IMS but to stick to standalone multiple 2U servers with Open-E SAN.
Do your calculation and explore if you really need X25-E instead of X25-M...