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C.2.2 RAID-1
RAID-1 is also known as mirroring or dual copy. It provides redundancy with better performance than a single disk, but requires real
disk capacity of two times the data size.
A RAID-1 array has two disk drive members. If the members have different capacities, the resulting RAID-1 array has the capacity
of the smaller member. Each data block of the array is written on each of the two members.
If one member fails, operations continue, to the good member. Performance is degraded for read operations (because read
operations cannot now be shared between the two members), and improved for write operations (because only a single member is
written). So a mixed workload may not show any change in overall performance. When a member returns or it is replaced (either
manually or automatically by the hot-spare mechanism), a rebuild occurs. This rebuild is performed in parallel with any activity to the
array.
SSA RAID Adapter Installation and User's Guide.
RAID-1
_ Copyright IBM Corp. 1996
C.2.2 - 1