USB 2.0 connection How to make three external hard disks RAID 5

Ubuntu Linux Server (Dapper)USB 2.0 connection It seems possible to operate three external hard disks as RAID 5. Speaking of cheapness, it may be cheap.

A movie actually running is here.
TechEBlog >> USB 2.0-Based RAID 5 Solution

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Because it is a USB connection, it seems to be able to hot swap once. In this example, I use three 320 GB hard disks of Western Digital. What about the cost performance, what is the structure suitable for this?