12.5

A database administrator can choose how many disks are organized into a single RAID 5 array. What are the trade-offs between having fewer disks versus more disks, in terms of cost, reliability, performance during failure, and performance during rebuild?

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Fewer disks has higher cost, but with more disks, the chance of two disk failures, which would lead to data loss, is higher. Further, performance during failure would be poor since a block read from a failed disk would result a large number of block reads from the other disks. Similarly, the overhead for rebuilding the failed disk would also be higher, since more disks need to be read to reconstruct the data in the failed disk. 😎