Added HowTo for Software RAID

[Chris Turner]

On 07/30/11 12:03, Mark Doe wrote:
I just added a small software RAID howto with natacontrol command. please
help to get rid of the typos and male it more complete - thanks
Thanks for the contribution - a good overview to start!

my (personal) thoughts:

Think the part about checking the source code for other options can be nixed -
IIRC I don't think the raid5 code actually works but the header bit is a placeholder -
checking src/sys/dev/disk/nata/ata-raid.c seems to confirm this - perhaps someone
has other ideas?
so suggesting people deviate from the 'official' documentation is probably a bad idea

also:

might want to test/add a section about removing/hotswapping drives and rebuilding
the array to 'complete the picture'
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- Chris