Specifications

20 en | RAID Functions: Introduction SCSI to SATA RAID Subsystem | Administrator’s Manual
F.01U.027.802 | V1 | 2006.11 Bosch Security Systems
As illustrated above, Configuration A is a RAID5 logical drive consisting of 24 physical drives.
Configuration B is a logical volume made of four RAID5 logical drives.
Fig. 1.17 Logical Volume Composed of 4 Logical Drives Formed by 24 Physical Drives
Configuration B can help reduce the chance of encountering points of failure:
• Higher Redundancy: Configuration A has one dedicated spare, while Configuration B
allows the configuration of four spares. In Configuration B, the risk of simultaneous drive
failure in a logical drive is significantly reduced compared to Configuration A. The total
array capacity is comparatively smaller by the use of spares.
• Less Rebuild Time: The time during rebuild is a time of potential hazard. For example, a
RAID5 logical drive can only withstand single drive failure - if another drive fails during the
rebuild process, data will be lost. The time span for rebuilding a faulty drive should be
minimized to reduce the possibility of having two drives fail at the same time.
Configuration A is a large logical drive and takes a long time to rebuild. All members will
be involved during the rebuild process. In Configuration B, the time span is shorter
because only six members will participate when rebuilding any of the logical drives.
• Channel Failure Protection: Channel failure may sometimes result from unlikely matters
such as a cable failure. A channel failure will cause multiple drives to fail at the same time
and inevitably lead to a fatal failure. Using a logical volume with drives coming from differ-
ent drive channels can avoid this point of failure.