Open SCSI Integrator's Manual for NonStop S-Series Servers

Integrating Hardware
Open SCSI Integrator’s Manual for NonStop Servers—422988-002
3-4
SCSI Configurations on the PMF CRU and IOMF
CRU
Dual-Path Configuration
Figure 3-3 shows the dual-path configuration. Each device on the bus is accessed
through two SCSI SACs: one in each PMF CRU or IOMF CRU.
This dual-path configuration is more fault-tolerant than the single-path because each
device on the bus can be accessed using either SCSI SAC. Therefore, if one SCSI SAC
fails, any device on the bus still can be accessed, using the other SCSI SAC.
Note, however, that the application software must be written to automatically handle
switching to the other SCSI SAC in the event of failure.
Figure 3-3. Dual-Path SCSI Bus Configuration on PMF CRU or IOMF CRU
022CDT .CDD
PMF CRU or
IOMF CRU
Passthrough terminator
SCSI port
PMF CRU or
IOMF CRU
SCSI bus
Passthrough terminator
External device External device External device
SCSI port
SCSI bus SCSI bus SCSI bus