RAID and Subsystem Architectures Assigning Hosts to Storage
Mapping Hosts to Storage
– Fully redundant data paths
H2 H1 S1 Fabric 1 S1’ C1 C2 S2’ S2 Fabric 2
Loop 1
M1 M2
Loop 2
This example shows a configuration with fully redundant data paths to a LUN:
The LUN consists of a mirrored pair of disks--the primary disk (D1) and the mirror (D2). D1 and D2 are connected to different loops and to different controllers (C1 and C2). In the fabric, C1 and C2 are attached to different fabrics through S1-S1’ and S2-S2’.
At the host, S1 and S2 are attached to different HBAs (H1 and H2).
In this architecture, commonly referred to as Controller Centric, the logical unit can only be accessed through one controller at a time. The other controller is considered in standby mode for this logical unit. It can be active for other logical units defined in the subsystem.
It is important to understand the controller behaviour when we consider HBA multipathing options. In this case it would be best to use manual LUN traffic distribution as opposed to dynamic per I/O load balancing.