sentence: Many drives fail because of mechanical problems.
sentences_before: In practice, however, the drives were often bought together.
sentences_after: The older a drive is, the more worn are its mechanical parts. Mechanical parts that are old are more likely to fail than those that are younger. This means that drive failures are no longer statistically independent. In practice, there is a chance that a second disk will also fail before the first has been recovered. This means that data loss can occur at significant rates, in practice.
concept_name: drive
headings: RAID Problems with RAID Linked failures
categories: Storage devices