IBM ServeRAID User Reference page 40

When you replace a failed drive, the ServeRAID controller can rebuild all the RAID
level-1, level-1E, level-5, and level-5E logical drives automatically onto the
replacement physical drive. However, any data stored in a failed RAID level-0
logical drive is lost.
Although the risk of data loss is present, you might want to assign RAID level-0 to a
logical drive to take advantage of the speed this RAID level offers. You can use this
logical drive to store data that you back up each day and can re-create easily. You
also might want to use a RAID level-0 logical drive when you require maximum
capacity.
RAID level-0 offers the following advantages and disadvantages.
Understanding RAID level-1
RAID level-1 uses data mirroring. Two physical drives are combined into an array,
and data is striped across the array. The first half of a stripe is the original data; the
second half of a stripe is a mirror (that is, a copy) of the data, but it is written to the
other drive in the RAID level-1 array.
RAID level-1 provides data redundancy and high levels of performance, but the
storage capacity is diminished. Because the data is mirrored, the capacity of the
logical drive when assigned RAID level-1 is 50% of the array capacity.
RAID level-1 requires two physical drives.
The following illustration shows an example of a RAID level-1 logical drive.
Start with two physical drives.
Create an array using the two physical drives.
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IBM ServeRAID: User's Reference, Version 5.10
Advantages
v Substantial speed enhancement
v Maximum utilization of physical drive
storage capacity, because no room is
taken for redundant data or data-parity
storage
Disadvantages
No data redundancy, resulting in data loss in
the event that a physical drive fails