Dot Hill Systems SANnet II 200 - Manual (Page 9)

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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