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RAID 0 (Commonly Used) This method is the fastest because all read/ write heads are constantly being used without the burden of parity or duplicate data being written. A system using this method has multiple disks, and the information to be stored is striped across the disks in blocks without parity. This RAID level only improves performance; it does not provide fault tolerance.


RAID 1 (Commonly Used) This level uses two hard disks, one mirrored to the other (commonly known as mirroring; duplexing is also an implementation of RAID 1). This is the most basic level of disk fault tolerance. If the first hard disk fails, the second automatically takes over. No parity or error-checking information is stored. Rather, each drive has duplicate information of the other. If both drives fail, a new drive must be installed and configured, and the data must be restored from a backup.


RAID 2 At this level, individual bits are striped across multiple disks. One drive (designated as the parity drive) in this configuration is dedicated to storing parity data. If any data drive (a drive in this configuration that is not the parity drive) fails, the data on that drive can be rebuilt from parity data stored on the parity drive. At least three disk drives are required in this configuration. This is not a commonly used implementation.


RAID 3 At this level, data is striped across multiple hard drives using a parity drive (similar to RAID 2). The main difference is that the data is striped in bytes, not bits as in RAID 2. This configuration is popular because more data is written and read in one operation, increasing overall disk performance.

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