HP A3550A - High Availability Disk Arrays Model 20 Storage Enclosure User Manual page 100

Disk Array Configurations
Configuration type
Basic
One host
One SCSI-2 adapter
One SCSI-2 bus
One SP
Two-SP
One host
One SCSI-2 adapter
One SCSI-2 bus
Two SPs
Multi-bus (HP-UX
10.x and later)
Two hosts
Two SCSI-2 adapters
(one per host)
Two SCSI-2 buses
(one per host)
Two SPs
Features
Applications can continue to run after the failure of a single disk module
within a physical disk unit (LUN). Applications cannot continue to run if an
SP, SCSI-2 adapter or external SCSI-2 bus fails.
Provides the same features as the basic configuration, but with better
performance and higher availability. Applications can continue to run if a
single disk module fails.
With HP-UX 10.x, if one SP fails, ownership of the failed SP's LUNs can
automatically transfer to the remaining operational SP. If properly
configured, these operations are transparent to the user. Auto-trespass is
not available on HP-UX 9.05/9.07. If the SCSI-2 adapter or external
SCSI-2 bus fails, no I/O operations are possible between the host and
the array.
Resembles two basic configurations side-by-side and provides modest
high availability with the external SCSI-2 buses not shared between two
hosts. Applications can continue to run if a disk module fails.
If a host adapter fails, the adapter on the other host can only access its
own LUNs. The System Administrator must manually change the path
and SP ownership of the LUNs for the failed SP or failed host adapter by
using Grid Manager. No automatic transfer of LUN ownership or path
takes place for this configuration type.
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