Option B (Correct):The output shows that the RAID array is in a "degraded, recovering" state, which means one of the devices failed, and the RAID is currently rebuilding with a spare device. When a RAID-5 array is in a degraded state, its read and write performance is reduced because it cannot utilize all disks in parallel, and data is being rebuilt.

Option C (Correct):The output indicates that/dev/sdf1is marked as "spare rebuilding." This implies that a new spare device has been added to the RAID array to replace a previously failed device, and it is in the process of rebuilding to restore redundancy.

Option A (Incorrect):The state of the RAID array is "degraded," which indicates that a RAID device is still being rebuilt. The failed device has not yet returned to normal operating status.

Option D (Incorrect):No extra device was added to increase the RAID set's size. Instead, a spare device was added to replace a failed one.

Option E (Incorrect):Both read and write performance are sub-optimal in a degraded RAID-5 state because data is being rebuilt using the remaining active devices.

Oracle Linux Reference:For more information, refer to:

Oracle® Linux 8: Managing Storage Devices

man mdadmfor details on managing RAID arrays.