HP Array Controller HSG V8.7 Software - Manual (Page 90)

Power Verification and Addressing
4–4 UltraSCSI RAID Enclosure
This action—removing power from the enclosure—duplicates an
EMU function and ensures optimum subsystem performance and
integrity.
PVA Operation
Most PVA operations occur automatically and do not require user
intervention. The following sections define major PVA operations.
EMU Installation Monitoring
If the EMU is removed or installed incorrectly (for example, not fully
seated), the PVA detects this condition and sounds the PVA audible
alarm. This alarm continues until the PVA senses that an operational
EMU is present.
Caution
Removing the EMU and PVA at the same time will cause
the system to RESET and cause conflicts between the
enclosures due to duplicate SCSI bus ID settings.
Disk Drive SBB Device IDs
The 24 disk drive SBBs in each enclosure are arranged on 6 vertical
buses in 4 horizontal shelves. All six devices on the same horizontal
shelf use the same device address or ID, but each device uses a
separate vertical bus. See Figure 4–4 for the master enclosure disk
drive SBB device IDs.