I had a server that had been running for 8 years on the same mirrored desktop-quality 40GB drives, 24/7, without a hiccup. I replaced the power supply and fans more than once during that period, but the drives never failed. Finally replaced the server with new hardware and virtualized the old server on it. The point is that you never can tell with hard drives. I've had them fail soon after installation, and I've had them last for years. I do tend to always use enterprise-rated drives now in servers, but it's no guarantee they'll last longer.