It's counterinturitive, but our media (e.g. CD's) are life-limited (http://www.zdnet.com/are-your-cds-dying-7000029547/?s_cid=e539&ttag=e539&ftag=TRE17cfd61
RAID's obviously represent an array of multiple drives which contain duplicate (backup data). If one HD has a mechanical failure, the data remains intact on another drive. However, a virus may be copied from one drive to the other before you know you have one Â so all your backups may be jeopardized. Also, damage (fire, wind, water) to your home/computer (mirrored array) would leave you without a backup.
Mirrored drives make sense if you're going to be adding or changing data on a routine basis, but if you're like me, I've already accumulated most of my favorite music and my library remains fairly static Â adding a few CD's now and again. This makes manually creating a duplicate drive not that difficult when those few times arise, when I need to add something new.
I maintain my music on several hard drives, some installed in my Windows PC, all the rest stored in-house or off site Â don't want to lose the time spent ripping the +28K tracks that I have.
I buy internal hard drives and external docking units for internal hard drives. These docks are plug and play and most are "hot swappable". In my audio room to connect to my Mac Mini, I use one from this company: http://www.newertech.com/products/voyagerq.php
For the hard drive to Mac mini connection used in my audio room, Firewire is (sonically) preferable, so I bought a dock with that capability. I also have a similar dock that I use for my Windows machine, only it doesn't have firewire capability, which makes it more reasonably priced (i.e. the more connections [USB, SATA, Firewire etc.] the higher the price of the dock.
BTW, if you don't need a firewire connection, a USB or SATA dock can be used on both a Windows or Apple machine.I like using USB/ESATA/Firewire hard drive docks.
My audio files are maintained as AIFF's and FLAC's. I like the latter because it is an open source CODEC and useable most everywhere. For track back-up purposes, always rip to a lossless format -- i.e. never rip to a lossly format (such as MP3).
I treasure my Tags (metadata), so although before Computer Audio, I did rip to WAV's, I no longer do so.
For multiple CODECS (i.e. WAV, AIFF, FLAC, MP3 etc.) dBpoweramp is a handy Windows based ripper and CODEC converter, because it will rip 1-CD to two different CODECS simultaneously. And it provides 3-different metadata on-line sources for comparison purposes, with an AccurateRip feature that confirms that your rip either is, or isn't identical to its database of other rips of the same CD.