Predicting SCSI Disk failures

Hi,

I was interested in knowing how are SCSI disk failures predicted? I know
there are some SMART disks which can give out some Additional Sense Data
that would indicate that the disk is going bad.
What algorithms are use and what parameters are considered?
Are there softwares that do such predictions on well-known OSes - W2K ,
Unix(s) and are they open-source?
Are there any documents / research articles/links on Disk Failure
Predictions?

Thanks
asheesh