Hardware Tuning:Choice of RAID Level To use RAID 1 or RAID 5? Depends on ratio of reads and writes RAID 5 requires 2 block reads and 2 block writes to write out one data block If an application requires r reads and w writes per second RAID 1 requires r+2w l/O operations per second RAID 5 requires:r+4w l/O operations per second For reasonably large r and w,this requires lots of disks to handle workload RAID 5 may require more disks than RAID 1 to handle load! Apparent saving of number of disks by RAID 5(by using parity,as opposed to the mirroring done by RAID 1)may be illusory! Thumb rule:RAID 5 is fine when writes are rare and data is very large, but RAID 1 is preferable otherwise If you need more disks to handle I/O load,just mirror them since disk capacities these days are enormous! Database System Concepts-6th Edition 24.11 @Silberschatz,Korth and SudarshanDatabase System Concepts - 6 24.11 ©Silberschatz, Korth and Sudarshan th Edition Hardware Tuning: Choice of RAID Level To use RAID 1 or RAID 5? Depends on ratio of reads and writes  RAID 5 requires 2 block reads and 2 block writes to write out one data block If an application requires r reads and w writes per second RAID 1 requires r + 2w I/O operations per second RAID 5 requires: r + 4w I/O operations per second For reasonably large r and w, this requires lots of disks to handle workload RAID 5 may require more disks than RAID 1 to handle load! Apparent saving of number of disks by RAID 5 (by using parity, as opposed to the mirroring done by RAID 1) may be illusory! Thumb rule: RAID 5 is fine when writes are rare and data is very large, but RAID 1 is preferable otherwise If you need more disks to handle I/O load, just mirror them since disk capacities these days are enormous!