/boot is not required as a partition.
However, this is where the kernel image is stored that you load during boot-up, and (on the ix86 architecute) some old BIOSes cannot load this image if it appears after the first 1024 cylinders. So to get around this problem, /boot is created within the first 1024 cylinders instead. If your BIOS is more recent, then you don't need this.
You can use the fdisk
command to list the actual, physical partitions on your hard disk. I think you'll find that hda5 is actually a swap partition, unless you deliberately didn't create one. The swap partition is now used for two reasons; swapping data out of RPM when you run out of space (effectively giving much more RAM at a spall performance penalty), and swapping data out of RAM to make more room for caching the hard disk (in turn speeding up disk operations).
The advantage of not
having a swap partition is that your latency will always be low; i.e.
graphical programs, web servers and the like will always respond to requests as quickly as possible, which typically makes them seem faster.
The main advantage of having a swap partition are that you are less likely to have programs crash due to a lack of memory. But there's also a performance increase for disk-bound non-interactive tasks, such as for a disk server, or for a web server that serves large, static files.
You'll find a software-RAID HOWTO on www.tldp.org.
Raid devices start counting at zero, so I suspect you will want to create md0, which will in turn use two or more partitions (for both speed and protection, these should be on different disks or you don't really gain anything).
Btw, the kernel effectively uses RAID-0 to combine swap partitions on different hard disks, so there's no advantage to using a RAID-0 device for swap partitions.