How is disk reliability addressed in RAID levels? Give a comparative analysis of RAID $4$ and RAID $5$ regarding read efficiency, write efficiency, fault tolerance, and usable capacity.

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b$)$ A disk drive spins at $9600$ RPM and has $2048$ cylinders and $7$ heads. Each track contains $221$ bits. Each sector contains $2048$ bytes. An entire sector must be read so that the data integrity can be checked and errors corrected, if necessary. How much time will it take to read one sector? Assume the R$/$W head is already over the desired track. $$