Hosting on powerful servers with multiple CPUs and up to 128 CPU cores per system. They have hundreds of Gigabytes of RAM and 40 Gbit/s connectivity giving the server a total of 4GB/s read/write speed.
These are RAID10 based servers (from 4 to 12 hard drives per server).
Thus, the servers stay up even if TWO drives happen to fail at the same time.
2016: Using SSD drives, up to 50 times faster than the normal HDDs most companies use.