Hardware RAID Levels

RAID Level	Minimum Number of Drives	Description	Strengths	Weaknesses
RAID 0	2	Data striping without  redundancy	Highest performance	No data protection; One drive fails, all data is lost
RAID 1	2	Disk mirroring	Very high performance; Very high data protection; Very minimal penalty on write performance	High redundancy cost overhead; Because  all data is duplicated, twice the storage capacity is required
RAID 2	Not used in LAN	No practical use	Previously used for RAM error  environments correction (known as Hamming Code ) and in disk drives before the use of embedded error correction	No practical use; Same performance can be achieved by RAID 3 at lower cost
RAID 3	3	Byte-level data striping with dedicated  parity drive	Excellent performance for large, sequential data requests	Not well-suited for transaction-oriented network applications; Single parity drive does not support multiple,  simultaneous read and write requests
RAID 4	3 (Not widely used)	Block-level data striping with dedicated  parity drive	Data striping supports multiple  simultaneous read requests	Write requests suffer from same single  parity-drive bottleneck as RAID 3; RAID 5 offers equal data protection and  better performance at same cost
RAID 5	3	Block-level data striping with  distributed parity	Best cost/performance for  transaction-oriented networks; Very high performance, very high data protection;  Supports multiple simultaneous reads and writes; Can also be optimized for  large, sequential requests	Write performance is slower than RAID 0  or RAID 1
RAID 0/1	4	Combination of RAID 0 (data striping) and  RAID 1 (mirroring)	Highest performance, highest data  protection (can tolerate multiple drive failures)	High redundancy cost overhead; Because  all data is duplicated, twice the storage capacity is required; Requires minimum of four drives
RAID 1/0	4	Combination of RAID 1 (mirroring) and  RAID 0 (data striping)	Shares the same fault tolerance as RAID 1 (the basic mirror), but compliments said fault tolerance with a striping mechanism that can yield very high read rates	High redundancy cost overhead; Because  all data is duplicated, twice the storage capacity is required; Requires minimum of four drives