Explanation
To calculate the minimum number of disks needed for this application, we need to consider the RAID levels and their disk requirements. RAID 1 requires a minimum of two disks and provides mirroring, which means that data is duplicated on both disks. RAID 5 requires a minimum of three disks and provides striping with parity, which means that data is distributed across all disks with one disk storing parity information for error correction. RAID 5 can tolerate one disk failure without losing data. To create a 10GB RAID 1 array for log files, we need two 10GB disks. To create a 20GB RAID 5 array for data files, we need four 10GB disks (three for data and one for parity). To create a 20GB RAID 5 array for the operating system, we need another four
10GB disks (three for data and one for parity). Therefore, the total number of disks needed is 2 + 4 + 4 = 10.
However, since we can use different RAID levels for different partitions on the same disk, we can optimize the disk usage by using only eight disks as follows: Disk 1: 10GB RAID 1 (log files) + 10GB RAID 5 (data files) Disk 2: 10GB RAID 1 (log files) + 10GB RAID 5 (data files) Disk 3: 10GB RAID 5 (data files) + 10GB RAID 5 (OS) Disk 4: 10GB RAID 5 (data files) + 10GB RAID 5 (OS) Disk 5: 10GB RAID 5 (parity for data files) + 10GB RAID 5 (OS) Disk 6: 10GB RAID 5 (OS) + unused space Disk 7: 10GB RAID 5 (parity for OS)
+ unused space Disk 8: unused space References: https://en.wikipedia.org/wiki/Standard_RAID_levels