It seems that the EFAX 8TB, 10TB, and 12TB drives, and the EFFX 14TB drives all spin at 7200 rpm (and always have), but were previously marketed as 5400 rpm drives because that was the 'class' they fitted in.
I see some posts where folk comment that new drives run hotter or consume more power or make more noise than smaller drives when swapped - maybe this is the reason. Either way, maybe double check the real spin speed of what you are fitting rather than the marketing literature. But maybe also, I am sure some users have same capacity drives with differing rotational speeds in the same array.For select products, Western Digital has published RPM speed within a “class” or “performance class” for numerous years rather than publishing specific spindle speeds. We also fine-tune select hard drive platforms and the related HDD characteristics to create several different variations of such platforms to meet different market or application needs. By doing so, we are able to leverage our economies of scale and pass along those savings to our customers. As with every Western Digital product, our product details, which include power, acoustics and performance (data transfer rate), are tested to meet the specifications provided on the product’s data sheet and marketing collateral.