Adaptec 1966600 User Guide - Page 87

Installing the DuraStor Storage Subsystem DuraStor 7220SS storage subsystem's without the cost of external hardware, other than cables. DuraStor FC RAID Appliance Host 1 Host Link 1 FC HBA Host 2 FC HBA Host Link 2 P2 HUB P1 HUB P3 P4 LUN 2 CH0 FC2 Passive CH1 FC1 LUN 2 Active CH2 Controller 2 CH3 LUN 1 FC1 Active FC2 LUN 1 Passive Controller 1 CH0 T CH1 T CH2 T CH3 T CH0 Up to 12 Disk Drives CH1 Up to 12 Disk Drives CH2 Up to 12 Disk Drives CH3 Up to 12 Disk Drives Figure 3-48 Active-Active Single-Port Hubs Enabled SAN Configuration Not Supported In the active-active dual-port configuration with two independent hubs or the internal hub, two single-ported hosts are not supported. The issue with this configuration is that if a controller fails, each host loses access to one of the LUNs. For example, if Controller 1 fails, Host 1 can no longer access LUN 2, because Port 2 on Controller 2 has changed from presenting its own LUNs to presenting Controller 1's LUNs. A need for this SAN configuration can arise if multiple single-ported hosts need access to LUNs from both controllers, and two hubs are desired to improve performance by decreasing loop access contention. Note that this SAN is only partially fault-tolerant because the hubs and controllers have redundant hardware, but the hosts do not. The problem with this configuration can be overcome by using a single switch at the cost of replacing the two hubs with a switch. If loop access contention is not an issue, then the single hub configuration works as well. 3-53