G-Speed Shuttle XL 36 TB TB3 Only 175MB/s Write?

G-Technology G-SPEED & G-SAFE
1

My G-Speed Shuttle XL 36TB Tunderbolt 3 Only has 175MB/s Write and around 680/MB/s Read.
30 TB in RAID 5
Used space is 17,5 TB

How can I fix this?