I have a MyCloud EX2 Ultra with 2 4TB Seagate SkyHawk drives running in RAID 1.
The write speeds are incredibly slow. I am trying to migrate my 170 GB photo library to it from my laptop. My laptop has a fast SSD.
They are connected by a gigabit connection to a gigabit switch (I have tested this) but the write speed is usually 3-10 MB/s which makes large transfers take FOREVER.
Bear in mind that every file also requires entries in the file allocation table. You’re also creating folders. Judging by the size of your library, you have a LOT of files and a LOT of folders. These “extra” writes may only take milliseconds but it adds up over 1,000’s of files/folders.
As another data point, uploading 24 gigs worth of photos (7,465 files, 348 folders) from my desktop (w/SSD) to my EX4 (4x2TB) on gigabit through my non-managed switch using short runs of Cat 6 cable yields about the same upload speed range The speed varies quite a bit during the transfer. I do have about 6 gb of .MOV files in there so the speed picks up a bit when it hits those.
If I upload only large videos, I get about 30-40mbps. You may want to try uploading a large video file to compare.
I partially fixed the solution. I disabled cloud access during the transfer which brought it to 50-60 MB/s. And then it took several days to index all of the files and generate previews aftewardcs