User's Manual

Troubleshooting 122
Disadvantages:
• This method is expensive, because many drives are needed for fault tolerance.
• Only half of the total drive capacity is usable for data storage.
RAID 1 (ADM) and RAID 10 (ADM)
In RAID 1 (ADM) and RAID 10 (ADM) configurations, data is duplicated to two additional drives.
When the array contains only three physical drives, the fault-tolerance method is known as RAID 1 (ADM).
When the array has more than three physical drives, drives are mirrored in trios, and the fault-tolerance
method is known as RAID 10 (ADM).
In each mirrored trio, the physical drives that are not busy answering other requests answer any read
requests that are sent to the array. This behavior is called load balancing. If a physical drive fails, the
remaining two drives in the mirrored trio can still provide all the necessary data. Several drives in the array
can fail without incurring data loss, as long as no three failed drives belong to the same mirrored trio.