RAID 1 consists of an exact copy (or mirror) of a set of data on two or more
disks; a classic RAID 1 mirrored pair contains two disks. This
configuration offers no parity, striping, or spanning of disk space across
multiple disks, since the data is mirrored on all disks belonging to the
array, and the array can only be as big as the smallest member disk. This
layout is useful when read performance or reliability is more important than
write performance or the resulting data storage capacity.
RAID 5 consists of block-level striping with distributed parity. Unlike in
RAID 4, parity information is distributed among the drives. It requires that
all drives but one be present to operate. Upon failure of a single drive,
subsequent reads can be calculated from the distributed parity such that no
data is lost.RAID 5 requires at least three disks.