g Consider an RAID-5 storage with 5 disk drives. A block read takes 10 time units, a block write takes 5 time units, and computing an XOR result of two blocks takes 1 time unit. Assume only one XOR operation can be performed each time (i. e., XOR operations cannot be done in parallel). A stripe (a row) has four data blocks (A, B, C, and D) and a parity block P, which are stored in the five disks, one in each disk respectively. If we need to write one data block A, give two methods to update this stripe in the RAID-5 storage. Explain each method step by step, and calculate the corresponding time cost that is needed for each method to complete the operations.

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