Chapter 3. Data Protection: RAID
In the late 1980s, rapid adoption of computers for business processes stimulated the growth of new applications and databases, significantly increasing the demand for storage capacity. At that time, data was stored on a single large, expensive disk drive called Single Large Expensive Drive (SLED). Use of single disks could not meet the required performance levels, due to their inherent limitations (detailed in Chapter 2, Section 2.4, "Fundamental Laws Governing Disk Performance").
HDDs are susceptible to failures due to mechanical wear and tear and other environmental factors. An HDD failure may result in data loss. The solutions available during the 1980s were not able to meet the availability and performance demands of applications.
An HDD has a projected life expectancy before it fails. Mean Time Between Failure (MTBF) measures (in hours) the average life expectancy of an HDD. Today, data centers deploy thousands of HDDs in their storage infrastructures. The greater the number of HDDs in a storage array, the greater the probability of a disk failure in the array. For example, consider a storage array of 100 HDDs, each with an MTBF of 750,000 hours. The MTBF of this collection of HDDs in the array, therefore, is 750,000/100 or 7,500 hours. This means that a HDD in this array is likely to fail at least once in 7,500 hours.
RAID is an enabling technology ...
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