Your friend's points are all true, and are the sort of thing that enterprise storage vendors like to fret over. New, high-end drives are now getting extensions that provide extra parity bits and the like for end-to-end data integrity.

BUT.. for real-people, SATA and/or UDMA-IDE is good enough. The drives, internally, always use massive ECC on the data. So if they return data, you are assured it is "parity-corrected".

The reason for SATA and/or UDMA-IDE, is that those interfaces also assure CRC protection on the link between the drive and the host controller. So it is protected against most bit errors on that path, too.

The only thing RAID5 buys over RAID1 here, is protection between the controller and the system memory. Which really isn't meaningful.

Note also, that anything attached with USB has _no_ parity/crc protection over the USB cable..

Cheers