810i write speed very slow up to 4MB/s write speeds

Setup: Hyper-V VM Server 2019 core set up as a data share server. iSCSI connection to 810i.
3x SSD 240GB each
5x HDD 14TB each
Carved out 8TB volume and attached iSCSI to target VM.
Running Robocopy session to copy data over from older data share server.
Transfers capping out at 4MB/s write throughput.
Our older 800i outperforms the newer 810i significantly.
In addition, I can use drive scanning software (TreeSize) on older Drobo resulting in complete scan 3.8TB finishing in roughly 30sec. Scanning new drive will get up to around 500GB within an hour.
Any suggestions?