Most of our raids were built using Western Digital disks WD5000YS. When I ordered some more disks, the ones I received were WD5000AAYS. I sent Western Digital email asking if these disks are interchangable with the ones in our raid and according to them, they are.
Dear Mary, Thank you for contacting Western Digital Customer Service and Support. Please see the links below for specifications of each product. You will see that they are indeed interchangeable. WD5000YS http://wdc.com/en/products/products.asp?driveid=238&language=en WD5000AAYS http://wdc.com/en/products/products.asp?driveid=331&language=en Sincerely, Peter K. Western Digital Service and Support http://support.wdc.com