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.
Under Mac OS X 10.3 and 10.4, a volume greater than 2TB will show as a 2TB volume due to a limitation in Apple's ATA layer (just above the driver). Sonnet plans to provide a 10.4 fix in the next driver release. Under Mac OS X 10.5 and 10.6, the full capacity of the RAID volume is available.