Raid 1; Figure 2-6. Diagram Of A Raid 1 Write - Compaq StorageWorks RAID Array 3000 Controller Shelf User Manual

RAID 1

RAID 1 (also known as mirroring or shadowing) takes data sent by the host
and duplicates it on all the drives in an array. The result is a high degree of
data availability, since you can lose all but one drive in the array and still have
full access to your data. This comes at a price: a RAID 1 array requires
multiple drives to achieve the storage capacity of a single drive. Figure 2– 6
shows a RAID 1 write.
Host Data
0010
1011
0110

Figure 2-6. Diagram of a RAID 1 write

A RAID 1 array will show up on the monitor as degraded when at least one
drive fails, even if two or more members of the redundancy group remain in
good working order. As long as at least two working drives remain in the
array, you may continue to run the array in degraded mode without putting
data in jeopardy.
Controller writes
data from cache
to all drives in
the array
RAID Array 3000 Controller 2-11
SHR-1055