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LaCie RAID Technology White Paper
neSTeD RAID LeveLS
RAID 0+1
RAID 0+1 is a secure RAID mode that is composed of a mirror of striped sets. RAID 0+1 arrays should have
disks in multiples of four. For LaCie products with five disks, in a RAID 0+1 array, the fifth disk will either be a
spare or will be unused. In the diagram, at right, array B is a mirror of array A.
Up to two disks can fail in a RAID 0+1 array without loss of data, as long as the failed disks are not part of dif-
ferent RAID 0 pairs. In reference to the diagram, disk 1 and disk 2 could fail and the data would be preserved
on disks 3 and 4.
Applications
RAID 0+1 provides good speeds because of
RAID 0 striping, but cuts the available capacity
of a device in half (assume all disks in the array
have the same capacity).
LaCie Products with RAID 0+1
Currently, no LaCie products
✦
RAID0
RAID0
RAID 0+1
A
B
A2
B2
C2
D2
A1
C1
D1
B1
A2
B2
D2
C2
A1
B1
C1
D1
Disk 1
Disk 2
Disk 3
Disk 4
RAID1
How RAID 0+1 Capacity Is Calculated
Each disk in a RAID 0+1 system should have
the same capacity.
Storage capacity in a RAID 0+1 configuration
is calculated by multiplying the number of drives
by the disk capacity and dividing by 2, or
C = n*d/2
where:
C = available capacity
n = number of disks
d = disk capacity
For example, in a RAID 0+1 array with four
drives each with a capacity of 1000GB, the
total capacity of the array would be 2000GB:
C = (4*1000)/2
RAID 0
RAID 1
RAID 3
RAID 3+Spare
RAID 5
RAID 5+Spare
RAID 6
RAID 0+1
RAID 10
Concatenation
JBOD
RAID Selection
