Few day ago I have bought new T20 and have found WD Blue (WD10EZEX) HDD inside. I was surprised and upset, as I do not accept this model as reliable server storage. Western Digital seems to have the same opinion and in its product sheet declares this HD as not recommended for business critical RAID.
I have asked the community about supported drives for T20 and got reply that the only 1TB WD supported is WD Black (WD1000XL).
However the local Dell support declared, that WD Blue is supported for T20. I tried to order two new Dell certified "server HDs" and got two more pieces of sh... eh, WD Blue.
Going to order unsupported but reliable WD RE drives.
***? It seems that client's trust is not worth US $20 for Dell...
I apologize for you getting the WD Blue drives your unsatisfied with, I too am not seeing them listed for the T20. As you said the only 1TB WD drive I see is the WD1000XL you spoke of. There are other 1TB supported, but from Seagate (pn # G1XNT), or Toshiba (pn# CW76M), but not WD.