Evercube
  Seriously — laptop disks in a server?

  It might sound strange, but laptop disks actually have a lot of 
  advantages for an always-on home server: they use less energy, run 
  very quiet, and take up little space. Although you pay roughly 
  double the price per gigabyte compared to 3.5" disks, you pay less 
  for electricity, and thus save money in the long run.

I seriously doubt the power savings over the lifespan of a hard drive (5-6 years) are greater than paying twice as much per gigabyte. After all, if they were, Backblaze themselves would be using 2.5" disks.In any event, the disks in a home storage server are going to be spending most of their time spun down, and drawing very little power.