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RAID 4 This level is similar to RAID 2 and 3 (striping with parity drive), except that data is striped in blocks, which facilitates fast reads from one drive. RAID 4 is the same as RAID 0, with the addition of a parity drive. This is not a popular implementation.

RAID 5 (Commonly Used) At this level, the data and parity are striped across several drives. This allows for fast writes and reads. The parity information for data on one disk is stored with the data on another disk, so if any one disk fails, the drive can be replaced and its data can be rebuilt from the parity data stored on the other drives. This works well if one disk fails. If more than one disk fails, however, the data will need to be recovered from backup media. A minimum of three disks is required. Five or more disks are most often used.

There are other levels of RAID, including RAID 53, 6, 7, and 10, but because they aren’t covered on the exam, we won’t discuss them here.

Backup Considerations

^Although you can never be completely prepared for every natural disaster or human foible that can bring down your network, you can make sure that you have a solid backup plan in place to minimize the impact of lost data. Even if the worst happens, you don’t have to lose days or weeks of work, provided that you have a solid plan in place. A backup plan is the set of guidelines and schedules that determine which data should be backed up and how often. A backup plan includes information such as:

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