Dual-Bus/Dual-Initiator Configuration
31
Dual-Bus/Dual-Initiator Configuration
The dual-bus/dual-initiator configuration provides the highest availability.
Each host has two SCSI-2 adapters, each of which connects by a separate
SCSI-2 bus to a separate SP in the storage system. Since this configuration
protects against a SCSI-bus cable failure, it provides higher availability than
the dual-initiator configuration. It is for enterprises requiring the highest
level of availability, such as the Oracle Parallel Server and FailSafe products.
For better performance with this configuration, you can bind some physical
disk units on one SP and the other physical disk units on the other SP. The
SP that binds a physical disk unit is its default owner. The route through the
SP that owns a physical disk unit is the primary route to the physical disk
unit. The route through the other SP is the secondary route to the physical
disk unit, and is available if a component in the primary route fails. Table 2-5
lists the error recovery features of the dual-bus/dual-initiator configuration.
Caution:
Because both hosts can access the same disk modules
simultaneously, the danger exists that one host can overwrite data stored by
the other. This configuration requires specific hardware and software (such
as a database lock manager) to protect the integrity of the stored data.
Table 2-5
Error Recovery: Dual-Bus/Dual-Initiator Configuration
Failing Component
Continue After
Failure?
Recovery
Disk module
Yes
With RAID levels specified at any level other than 0,
applications continue running. System operator replaces
module.
Storage-control
processor
Yes
I/O operations fail to disk units owned by the failing SP.
System operator can transfer control of the failed SP’s disk
units to the surviving SP, shut down the host, power the
storage system off and on, and reboot both hosts. When
convenient, Silicon Graphics SSE or other authorized service
provider replaces the SP, and the system operation can
transfer control of the disk units to the replacement SP.
Fan module
Yes
Applications continue running. System operator replaces
module.
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