Just got the MBP 2018 A1990 models shipped today, damn the combination of T2 and FileVault is lightning fast, after DEP enrollment, FV enabled there are no more encryption times. Nice!
*As for the disk controller? There isn’t one—or more accurately, the disk controller is built into the T2 itself. This gives the T2 complete control over internal storage on the iMac Pro. This has some major benefits in terms of speed and security. Every bit of data stored on an iMac Pro’s SSD is encrypted on the fly by the T2, so that if a nefarious person tried to pull out the storage chips and read them later, they’d be out of luck.
(For additional security, Apple strongly suggests you turn on FileVault, which ties SSD encryption to your password. This provides an additional level of security, because your disk can’t be decrypted without the proper hardware and your password.)
All this encryption happens invisibly, so the SSDs in the iMac Pro still operate at full speed—approximately 3GB per second.*