Managing RAID on Linux

Choosing Hard Drives

Hard drives represent the most challenging bottleneck in data storage. Unlike disk controllers, motherboards, and other components that make up a system, hard drives are unique because they contain mechanical components. This presents a complicated problem for engineers because the moving parts of hard drives limit the speed at which data can be stored and retrieved. Whereas memory and controllers, for example, are completely electronic and can operate at close to light speed, hard drives are much slower.

In general, it’s a good idea to use the same disks in an array whenever possible. But using identical disks might not be an option all the time. Disks are made of several parts that affect their overall performance. If a situation arises in which you are forced to mix different disks, then you will want to know how to best evaluate a new disk to ensure that it will function appropriately when added to an array.

Platters, tracks, sectors, and cylinders

Two mechanical parts that affect performance are found on every hard drive. Inside each drive are magnetic platters, or disks, that store information. The platters, of which most common hard disks have several, sit on top of each other, with a minimum of space between each platter. They are bound by a spindle that turns them in unison. The surface of each platter (they are double-sided) has circular etchings called tracks, similar to a phonograph record, with the important difference being that tracks on a hard disk ...