LENOVO ThinkSystem ST550 2.5" SATA/SAS 4-Bay Backplane kit (media bay conversion kit)
"Adds 4x 2.5-inch to media bay (replacing existing 5.25"" bays) to the ThinkSystem ST550
The kit contains the backplane and the necessary cables as well as the necessary 4x 2.5-inch drive-bay cage.
Connection to a RAID Controller or HBA is required"