Bitlocker (Windows 10) and USB memory key speed

Question

Like many others, I'm experiencing extremely slow transfer speeds with Bitlocker encoding using a USB memory key. I've not seen a satisfactory explanation let alone a solution anywhere online. These reports go back for many years now. 'Make sure your drivers are up to date' is not a helpful support comment.

I've measured speeds on the same Kingston USB memory key on an encoded Bitlocker partition vs an unencoded partition. Write speeds are roughly 10x slower using Bitlocker. Over the years I've used different versions of Windows (7, 10), all with updated drivers, and various USB memory keys using whole-drive or whole-parition Bitlocker encoding. Note that my USB key already has many files, not a unique use-case I'm sure but worth noting also for testing. Anecdotally, copying various sets of files can become even slower, the drive virtually becoming unresponsive for a long time. It seems calculating available space and listing files also seems very slow. I'm confident this is reproducible.

My questions are:

1. What is the issue with Bitlocker & Windows?
2. Is this going to be addressed (ever)?

Specifics:

OS: Windows 10 Pro 64-bit (Windows 7 before - various versions - always updated versions)

Application: Bitlocker / Windows Explorer as part of Windows

Hardware: Kingston DataTraveler G4 - DTIG4/128GB USB 3.1 Gen 1/USB 3.0 Flash Drive, 128 GB

Test results:

Test1: 10mb / 10 files (various sizes)

normal: 10s

bitlocker: 56s

factor: ~6x

Test2: 100mb / 77 files (photos)

normal: 7s

bitlocker: 125s

factor: ~18x

Answer 1

Please optimize the drive for better performance via properties in diskmgmt.msc

Does that change the speed?