(Q) How do you defrag the AS/400's Hard Drives
(A) STRDSKRGZ

(Q) What are the differences between Mirroring (RAID1) and RAID5?
(A) Raid5 is faster, and you have more usable disk space
    Raid1 needs 1b for each 1b you are protecting, whereas
    RAID5 needs 1b for each 8b you are protecting.