RAID 5

RAID 5

RAID 5 uses striping with parity information written across multiple drives to enable fault-tolerance with a minimum of wasted disk space. This level also offers the advantage of enabling relatively efficient performance on writes to the drives, as well as excellent read performance.

Striping with parity is based on the principle that all data is written to the hard drive in binary code (ones and zeros). RAID 5 requires at least three drives because this version writes data across two of them and then creates the parity block on the third. If the first byte is 00111000 and the second is 10101001, then the system computes the third by adding the digits together using this system:

1+1=0, 0+0=0, 0+1=1, 1+0=1

The sum of 00111000 and 10101001 is 10010001, which would be written to the third disk. If any of the disks fail, the process can be reversed and any disk can be reconstructed from the data on the other two. See Figure 9.5 for an illustration of the process. Recovery includes replacing the bad disk and then regenerating its data through the Disk Administrator. A maximum of 32 disks can be connected in a RAID 5 array under Windows NT.