With redundant controllers, the system can use the controllers in active/passive or active/active (recommended) mode. When a controller is configured as active/passive, only a single controller is used to process I/O, while the other controller passively stands by in case of failure.
When configured as active/active, both controllers actively process I/O. Each time a host writes information to one controller, it is automatically copied to the other for protection. If a controller were to fail while in an active/active configuration, the survivor automatically takes over all I/O from the failed controller until the failed controller is replaced. Using redundant active/active controllers also enables the online updating of controller firmware without host interruptions.
The presence or absence of controllers affects the scalability of an individual SANnet II 200 SCSI array. Enclosures with controllers can scale by adding one or two expansion enclosures, but enclosures without controllers cannot be expanded.
To remove a controller, loosen the small thumbscrews at each end then remove the controller by pulling it out from the enclosure. To install one, slide the controller into the enclosure until it stops and tighten the thumbscrew until secure. To maintain optimum cooling, avoid operating a SANnet II 200 SCSI array for more than a few minutes with a controller removed.
FIGURE 5: SANnet II 200 SCSI Array RAID Controller Diagram
Disk Modules
The SANnet II 200 SCSI array supports a variety of disks available in a number of capacities and speeds. Current choices include 36GB, 73GB and 146GB disk drives operating in Ultra160 SCSI
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