Final answer:
When a disk fails in a RAID configuration, rebuilding data is easiest with RAID level 1 due to its mirroring feature where each disk contains an exact copy of the other's data.
Step-by-step explanation:
If a disk fails in a RAID (Redundant Array of Independent Disks) configuration, the ease of rebuilding lost data varies depending on the RAID level. For RAID level 1, data rebuilding is the easiest, as this level uses mirroring; each disk has an exact copy of the data of the other disk. As a result, if one disk fails, the system can rebuild the lost data from the other disk without any data loss.
RAID levels 2, 3, and 4 are less common and involve more complex data rebuilding processes. RAID level 2 uses bit-level striping with Hamming-code parity, rarely used today. RAID level 3 uses byte-level striping with a dedicated parity disk, and RAID level 4 uses block-level striping with a dedicated parity disk. However, RAID level 1 is still the simplest in terms of rebuild simplicity and speed.