To determine the best RAID level for your servers, evaluate the read and write loads of all data types and then decide how much you can spend to achieve the performance and availability/reliability that your organization requires. Table 10 describes common RAID levels and their relative performance, reliability, availability, cost, capacity, and energy consumption. Table 10. RAID Trade-Offs Performance Reliability Availability Cost, capacity, and power JBOD Pros: Concurrent sequential streams to separate disks. Cons: Susceptibility to load imbalance. Pros: Data isolation; single loss affects one disk. Cons: Data loss after one failure. Pros: Single loss does not prevent access to other disks. Pros: Minimum cost. Minimum RAID 0 (striping) Two-disk minimum. Pros: Balanced load. Potential for better response times, throughput, and concurrency. Cons: Difficult stripe unit size choice. Cons: Data loss one failure. Single loss affects the entire array. Cons: Single loss prevents access to entire array. Pros: Minimum cost. Minimum RAID 1 (mirroring) Two-disk minimum. Pros: Two data sources for every read request (up to 100% performance Cons: Writes must update all mirrors. Pros: Single loss and often multiple losses (in large are survivable. Pros: Single loss and often multiple losses (in large do not prevent access. Cons: Twice the cost of RAID 0 or JBOD. Up to 2X power . )
RAID 0+1 (striped mirrors) Four-disk minimum. Pros: Two data sources for every read request (up to 100% performance Balanced load. Potential for better response times, throughput, and concurrency. Cons: Writes must update mirrors. Difficult stripe unit size choice. Pros: loss and multiple losses (in large are survivable. Pros: loss and often multiple losses (in large do not prevent access. Cons: Twice the cost of RAID 0 or JBOD. to 2X power . configurations configurations
RAID 5 (rotated parity) One additional disk required. Three-disk minimum. Pros: Balanced load. Potential for better read response throughput, and concurrency. Cons: Up to 75% write performance reduction because of Decreased read performance in failure mode. All sectors must be read for slowdown. Danger of data in invalid state after power loss and recovery. Pros: Single loss survivable; “in-flight” write requests might still become corrupted. Cons: Multiple losses affect entire array. a single loss, array is vulnerable until Pros: Single loss does not prevent access. Cons: Multiple losses prevent access to entire array. To application access might be slowed or stopped. Pros: Only one more disk to power. Cons: Up to 4X the power for write requests (excluding the idle power).
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