RAID Level Pros/Cons

RAID level pros and cons
RAID level	Characteristics	Minimum number of physical drives	Advantages	Disadvantages
0	Uses striping but not redundancy of data; often not considered “true” RAID	2	Provides the best performance because no parity calculation overhead is involved; relatively simple and easy to implement	No fault tolerance; failure of one drive will result in all data in an array being lost
1	Duplicates but does not stripe data; also known as disk mirroring	2	Faster read performance, since both disks can be read at the same time; provides the best fault tolerance, because data is 100 percent redundant	Inefficient high disk overhead compared to other levels of RAID
2	Disk striping with error checking and correcting information stored on one or more disks	Many	Very reliable; faults can be corrected on the fly from stored correcting information	High cost; entire disks must be devoted to correction information storage; not considered commercially viable.
3	Striping with one drive to store drive parity information; embedded error checking (ECC) is used to detect errors	3	High data transfer rates; disk failure has a negligible impact on throughput	Complex controller design best implemented as hardware RAID instead of software RAID
4	Large stripes (data blocks) with one drive to store drive parity information	3	Takes advantage of overlapped I/O for fast read operations; low ratio of parity disks to data disks	No I/O overlapping is possible in write operations, since all such operations have to update the parity drive; complex controller design
5	Stores parity information across all disks in the array; requires at least three and usually five disks for the array	3	Better read performance than mirrored volumes; read and write operations can be overlapped; low ratio of parity disks to data disks	Most complex controller design; more difficult to rebuild in case of disk failure; best for systems in which performance is not critical or that do few write operations
6	Similar to RAID 5 but with a second parity scheme distributed across the drives	3	Extremely high fault tolerance and drive-failure tolerance	Few commercial examples at present
7	Uses a real-time embedded operating system controller, high-speed caching, and a dedicated parity drive	3	Excellent write performance; scalable host interfaces for connectivity or increased transfer bandwidth	Very high cost; only one vendor (Storage Computer Corporation) offers this system at present
10	An array of stripes in which each stripe is a RAID 1 array of drives	4	Higher performance than RAID 1	Much higher cost than RAID 1
53	An array of stripes in which each stripe is a RAID 3 array of disks	5	Better performance than RAID 3	Much higher cost than RAID 3
0+1	A mirrored array of RAID 0 arrays; provides the fault tolerance of RAID 5 and the overhead for fault tolerance of RAID 1 (mirroring)	4	Multiple stripe segments enable high information-transfer rates	A single drive failure will cause the whole array to revert to a RAID 0 array; is also expensive to implement and imposes a high overhead on the system