User's guide for the Sonnet Fusion D500P 5-drive Serial ATA disk enclosure with port multiplier storage system. These directions apply to storage systems with drives.
Another manufacturer's previously-installed SATA driver may be accessing a Sonnet SATA card in error causing a drive access slowdown. For example, we have seen Fusion D400QR5 performance drop from 200MB/s to under 50MB/s in such circumstances. The solution is to remove the other manufacturer's SATA driver.