Hey man, with hardware nowadays I wouldn't worry about disk access speed or any performance metric, they're all more than enough to stream audio/video to multiple destinations.
FWIW, I have a simple system that uses a "silent" case that holds 8 drives, and some 4 port PCI SATA adaptors; Promise Technology, Inc. PDC20718 (SATA 300 TX4)
I happen to be comfortable with linux, but the same can be done with any OS these days.
A cron job mounts the redundant disk, rsync's one disk to another, then unmounts the backup disk in the middle of the night. I generally run this script manually immediately after copying a buncha shows onto the server just for paranoia.
When the pair is full I remove one disk for offline storage and insert another pair. I size the disks according to the best dollar to gig ratio of Seagates at the time.
The box has an audiophile 2496 card for stereo playing (ALSA driver) and uses windows network file sharing (via samba) to stream tunes elsewhere.
The organization part is 100% done in player software (mpd, amarok) via tags on the flac files and there's some minor directory stucture for file level organization.
Tagging flacs/converting shns is done with a modified etree script, flacify.
Its a simple system that's easily recoverable from most failure conditions, with no RAID horror possible.
The evolution of listening habits with instant, searchable, randomizable, categorized, sliced and diced access to all music is fantastic. There is no going back