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You can determine the best RAID for your servers by evaluating the read and write loads of the various data types and then deciding how much you are willing to spend to achieve the performance and availability/reliability that your organization requires. Table 8 describes common RAID levels and their relative costs, performance, availability, and reliability. 8. RAID Trade-Offs Performance Reliability Availability Cost and capacity JBOD Pros: Concurrent sequential streams to separate disks. Cons: Susceptibility to load imbalance. Pros: Data isolation; single loss affects one disk. Cons: Data loss one failure. Pros: Single loss does not prevent access to other disks. Pros: Minimum cost. RAID 0 (striping) Pros: Balanced load. Potential for better response times, throughput, and concurrency. Cons: Difficult stripe unit size choice. Cons: Data loss after one failure. Single loss affects entire Cons: Single loss prevents access to entire array. Pros: Minimum cost. Two-disk minimum. RAID 1 (mirroring) Pros: Two data sources for every read request (up to 100% performance boost). Cons: Writes must update all mirrors. Pros: Single loss and often multiple losses (in large configurations) are survivable. Pros: Single loss and multiple losses (in large configurations) do not prevent access. Pros: Twice the cost of RAID 0 or JBOD. Two-disk minimum. RAID 0+1 (striped mirrors) Pros: Two data sources for every read request (up to 100% performance boost). Balanced load. Potential for better response times, throughput, and concurrency. Cons: Writes must update mirrors. Difficult stripe unit size choice. Pros: Single loss and multiple losses (in large configurations) are survivable. Pros: Single loss and often multiple losses (in large configurations) do not prevent access. Pros: Twice the cost of RAID 0 or JBOD. Four-disk minimum.
RAID 5 (rotated parity) Pros: Balanced load. Potential for better read response times, throughput, and concurrency. Cons: Up to 75% write performance hit due to RMW. Read performance degrades in failure mode. All sectors that must be read for reconstruction; major slowdown. Danger of data in invalid after power loss and recovery. Pros: Single loss survivable; requests might still corrupt. Cons: Multiple losses affect entire array. After a single loss, array is vulnerable until reconstructed. Pros: Single loss does not prevent access. Cons: Multiple losses prevent access to entire array. To speed reconstruction, application access might be slowed or stopped. Pros: One additional disk required. minimum. RAID 6 (two separate erasure codes) Pros: Balanced load. Potential for better read response times, throughput, and concurrency. Cons: Up to 83% write performance hit due to multiple RMW. Read performance degrades in failure mode. All sectors must be read for reconstruction: slowdown. Danger of data in invalid state after power loss and recovery. Pros: Single loss survivable; "inflight" write requests might still corrupt. Cons: >2 losses affect entire array. After 2 losses, array is vulnerable until reconstructed. Pros: Single loss does not prevent access. Cons: >2 losses prevent access to entire array. To speed reconstruction, application access might be slowed or stopped. Pros: Two additional disks required. Five-disk minimum. The following are sample uses for various RAID levels: JBOD: Concurrent video streaming. RAID 0: Temporary or reconstructable data, workloads that tend to develop hot spots in the data, and workloads with high degrees of unrelated concurrency. RAID 1: Database logs, and critical data and concurrent sequential streams. RAID 0+1: A general-purpose combination of performance and reliability for critical data, workloads with hot spots, and high-concurrency workloads. RAID 5: Web pages, semicritical data, workloads without small writes, scenarios where capital and operating costs are an overriding factor, and workloads. dominated