Unfortunately I don't have the answer to your configuration questions but it's worth mentioning that RAID 1 is not a backup. If something disastrous happens to that PC both drives may be lost. And it's not unheard of to replace a failed drive only to have the intense array rebuild process kill another drive before the rebuild completes. So if your friend has important files they should be backed up periodically to separate hardware, preferably stored in another location.
On a related topic, he should consider buying a spare drive now. That way if there ever is a failure he has a drive to use for rebuild. Waiting until there is a failure to look for a replacement, waiting for it to be shipped, etc. is not fun.
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