Sans Digital Mobileraid MR8X Detailed User's Manual page 16

Definition of RAID Levels
best performance of any redundant array type. In addition, there is less performance
degradation during drive failure than in RAID 5 arrays.
Dual-level RAID achieves a balance between the increased data availability inherent in
RAID 1 and the increased read performance inherent in disk striping (RAID 0). These arrays
are sometimes referred to as RAID 0+1.
RAID 0 is typically defined as a group of striped
disk drives without parity or data redundancy.
RAID 0 arrays can be configured with large
stripes for multi-user environments or small
stripes for single-user systems that access long
sequential records. RAID 0 arrays deliver the
best data storage efficiency and performance of
any array type. The disadvantage is that if one
drive in a RAID 0 array fails, the entire array
fails.
RAID 1, also known as disk mirroring, is simply
a pair of disk drives that store duplicate data
but appear to the computer as a single drive.
Although striping is not used within a single
mirrored drive pair, multiple RAID 1 arrays can
be striped together to create a single large array
consisting of pairs of mirrored drives. All writes
must go to both drives of a mirrored pair so that
the information on the drives is kept identical.
However, each individual drive can perform
simultaneous, independent read operations.
Mirroring thus doubles the read performance of
a single non-mirrored drive and while the write
performance is unchanged. RAID 1 delivers the
Installation and Configuration Manual
SAS-to-SATA II RAID Subsystem
16