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+RAID 3 RAID level 3: "Parallel transfer disk w/ Parity" RAID level 3 stripes data across multiple drives, with an additional drive dedicated to parity, for error correction & recovery. The technology used for a dedicated parity disk is to store redundant information about the data on several data disks. RAID level 3 is an excellent choice for applicators which require single stream I/O with a high data transfer rate. RAID level 3 is optimal for applications in which large blocks of sequential data must be transferred quickly, these applications usually are: *RAID level 3 requires a minimum of 3 drives to initiate. +RAID5 RAID level 5: “Independent access array w/rotating Parity” When RAID level 5 technology is combined with cache memory to improve it’s write performance, the result can be used in any applications where general purpose disks would be suitable. For read only or read mostly application I/O loads, RAID level 5 performance should approximate that of a RAID level 0 array. In fact, for a given user capacity, RAID level 5 read performance should normally be slightly better because requests are spread across one more members than they would be in a RAID level 0 array of equivalent usable capacity. RAID level performs best in applications where data and I/O load characteristics match their capabilities. Those of which whose data availability is worth protecting, but the value of a full disk is questionable. *RAID level 5 requires a minimum of 3 drives to initiate. +RAID6 RAID level 6: “Disk Striping with Double Distributed Parity” RAID 6 stripes blocks of data and parity across an array similar to RAID 5. Instead of a single parity, RAID 6 calculates two sets of parity information for each parcel data. This results in improving the arrays fault tolerance. RAID 6 can be slower than RAID 5 in terms of writes due to the added overhead of more parity calculations, but may be slightly faster in random reads due to the spreading of data over one more disk. RAID 6 requires a minimum of four drives to implement." Advantages: Data is striped on a block level across a set of drives in a similar fashion as RAID 5 but a second set of parity is also calculated and written across all the drives. RAID 6 offers fault tolerance and drive-failure tolerance that can sustain multiple simultaneous drive failures making it ideal for mission critical applications. Disadvantages: RAID 6 requires a complex controller to implement and compensate for the high overhead of dual parity computations. Requires N+2 drives to implement because of the two dimensional parity scheme. Rebuilding significantly effects performance. Recommended Applications *RAID level 6 requires a minimum of 4 drives.
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