Managing RAID on Linux

Striping

Striping is a method by which data is spread across multiple disks (see Figure 1-3). A fixed amount of data is written to each disk. The first disk in the array is not reused until an equal amount of data is written to each of the other disks in the array. This results in improved read and write performance, because data is written to more than one drive at a time. Some arrays that store data in stripes also support redundancy through disk parity. RAID-0 defines a striped array without redundancy, resulting in extremely fast read and write performance, but no method for surviving a disk failure. Not all types of arrays support striping.

Figure 1-3. Striping improves performance by spreading data across all available disks.

Stripe-size versus chunk-size

The stripe-size of an array defines the amount of data written to a group of parallel disk blocks. Assume you have an array of four disks with a stripe size of 64 KB (a common default). In this case, 16 KB worth of data is written to each disk (see Figure 1-4), for a total of 64 KB per stripe. An array’s chunk-size defines the smallest amount of data per write operation that should be written to each individual disk. That means a striping array made up of four disks, with a chunk-size of 64 KB, has a stripe-size of 256 KB, because a minimum of 64 KB is written to each component disk. Depending on the specific RAID implementation, ...