Installation guide

Software Operation Manual
148
single point of failure.
6.1.3 Configuration & Connectivity
Redundant SAS raid subsystem implements ALUA (Asymmetric Logical Unit
Access) algorithm which allows Volume Sets can be accessed by only one
controller when both controllers are on-line. The controller which controls the
Volume Sets is the preferred controller and another controller is for standby. For
example, Volume Set #000 was controlled by the controller A and the redundant
SAS raid subsystem allows host server access Volume Set #000 only through
the controller A. The controller B would take over the data I/O if the controller A
is failed. Figure 1 shows the standard connectivity for a single volume.
Figure 1
Redundant SAS raid subsystem default assigns even Volume Sets to controller
A and odd Volumes Sets to controller B. For example, controller A is the
preferred controller for Volume Set #000 and controller B is the preferred
controller for Volume Set #001 and so on.
The method to configure RAID Sets is the same with the single controller
subsystem, such as creating RAID Sets, creating volume sets and etc. To
ensure the I/O redundancy, both two controllers must be connected to the host
server. Physical connectivity of redundant SAS raid subsystem was described
as follow.