Why pay OEM prices for SATA/SAS HDD interposers when you can get them much more cheaply from Bargain Hardware’s refurbished stocks.
SATA and SAS drive can work from the same controller, but the two interfaces work differently. SAS has a rich set of diagnostics and controls that are not available in the ATA standard. So when mixing SATA and SAS, it is necessary to make the SATA drive appear to be a SAS drive. The chip on the interposer does this.
Having decommissioned thousands of HP, Dell and IBM servers, Bargain Hardware most likely will have the HDD interposer you need in stock, tested and ready to go.