Having recently gone through a similar loop for all my data, media and HTPC requirements Ill offer you this:
Is "fail over" really that necessary to you ? Or could you actually cope with maybe a day or two of downtime in a worst case scenario ?
I asked myself the same question and I decided that I could survive with having to rebuild if I really had to. As a result the solution I came up with for my backup needs was:
1) Replaced power hungry Dell PowerEdge server and Pentium D HTPC with an Acer Revo !
2) Hooked up an IcyBox Dual SATA USB enclosure (2 * 1TB HDD) and a Western Digital Elements 500GB USB HDD to the Revo.
3) All movies and TV onto the HDDs in the Icy Box
4) All Music, Pictures and Documents to the WD Elements
5) EVERYTHING thats important to me is backed up to Carbonite; "Cloud backup" service.
Now the "cunning" bit:
My "important" work machine runs Acronis and automagically generates an image of the boot partition which is stored onto the WD HDD connected to the Revo. Other "bits and pieces" from my work machine are also backed up onto the same WD HDD. Remember this is then uploaded to Carbonite.
I then make use of all of the "unused" space on other devices that I own (a laptop and a netbook).
Using SyncBack I keep an up-to-date copy of my entire music and picture collections on my netbook and laptop.
I also have a complete copy of all of my "work stuff" synchornised between the WD HDD and my laptop.
Here are my failure scenarios:
"ergh" case - The HDD in my Revo dies:
Replace HDD, restore boot partition from Acronis which is located on a local USB HDD.
"annoying" case - My IcyBox dies taking the 2 SATA disks with it:
All of my movies and TV are lost; until I restore them from Carbonites service.
"omg" case - Someone steals my entire living room:
Restore everything except Movies and TV from other devices. Movies and TV are downloaded from Carbonite.
"seriously?" case - An EMP wipes out all electronics in my house:
Buy new hardware and restore everything from Carbonite.
Hopefully Ill never need the carbonite service but the whole offsite storage thing just seems better than purely relying on local RAID and USB disks; plus its not all that expensive.
No doubt theres a scenario that Ive missed but hey, when it happens...Ill cry