Spread Spectrum Clocking is a way to lower electromagnetic interference or EMI. This is important for storage solutions that are required to pass FCC and other agency certifications. All current Serial ATA disk drives implement SSC (some allow you to turn this feature on/off). However, some older SATA drives do not implement SSC. All Sonnet Serial ATA host adapter cards support SSC but will also work with disk drives that do not.
The new 3 Gigabit/second eSATA cards contain a rather large Marvell chip with the string "88SX6081" on it. Previous generation eSATA cards had a Marvell chip labeled "88SX5081". Additionally, you can check your Macintosh System Profile. When you select the installed eSATA card, the Device ID will show either "0x6081" or "0x5081".
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.
