RAID levels zero through five RAID comes in several flavors, levels zero through five. Each level is optimized for various capabilities, including improved performance of read or write operations, and improved data availability through redundant copies or parity checking. It provides basic disk striping without parity protection to catch errors, so while throughput is high, no redundancy is provided. Implementations should be relatively inexpensive because no extra storage is provided for parity information and because the software and firmware is not as complex as other RAID levels. If one disk in the array happens to fail, however, all data in the array is unavailable.
All data is written twice to separate drives.
The cost per megabyte of storage is higher, of course, but if one drive fails, normal operations can continue with the duplicate data. And if the RAID device permits hot-swapping of drives, the bad drive can be replaced without interrupting operations. Performance with RAID-1 is moderate, performing faster on reads than on writes. Striping increases throughput, and simultaneous reads from the two sets will mitigate the performance drag caused by writing everything two times. RAID-2 performs disk striping at the bit level and uses one or more disks to store parity information.