Your drive system is one of the places where bottlenecks can occur. All of your database information, boot code, swap space, and user programs live on the hard drives. Hard drives are speeding up, now topping 15,000 RPM and bus rates of over 160MB per second. Even at these speeds, drives are still much slower than RAM or your CPU, with requests to drives waiting for the drive to spin to the right location, read and/or write the data that is required, and send the answer back to the CPU.
To top this off, hard drives are one of the moving parts in your machine, and moving parts are more likely to fail over time than a solid state mechanism, like your memory or CPU. One of the reasons why power supplies have such low MTBFs is the fan that keeps the power supply cool has a low MTBF. Once the fan dies, it's only a matter of time before the power supply itself overheats and dies. Some systems overcome this by installing multiple power supplies, so if one dies, the others can take over. Fortunately for hard drives, this failover is available in the form of RAID (Redundant Array of Inexpensive Disks).
Then there are questions about the cost of differing systems versus their performance versus other options. We will take a look at these options throughout this chapter, starting with an overview of existing hard drive technology for Linux.