HP A3550A - High Availability Disk Arrays Model 20 Storage Enclosure User Manual page 109

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
4-2
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 continue to run after
the failure of a single disk module.
HP-UX 9.04
If one SP fails, the System Administrator must reassign ownership of
the failed SP's LUNs to the operational SP by using Grid Manager.
Also, the path to the operational SP must be used and can be
changed by way of LVM. Once these changes have been made,
access to all LUNs on the array is possible. If the SCSI-2 adapter or
external SCSI-2 bus fails, no I/O operations are possible between the
host and the array.
HP-UX 10.x
If one SP fails, ownership of the failed SP's LUNs can transfer
automatically to the remaining operational SP. If a primary and an
alternate path have been configured in LVM, LVM can switch
automatically to the alternate path. These operations are transparent
to the user. If the SCSI-2 adapter or external SCSI-2 bus fails, no I/O
operations are possible between the host and the array.