System Startup, Configuration, and Shutdown Reference Manual (32650-90907)

Appendix G
UPS and UPS Monitor/iX Software
Configuring a UPS Device
220
System Behavior When AC Power Fails
Whenever input AC power to any UPS device fails, the UPS hardware switches to internal battery operation
to continue to deliver output AC power to the computer equipment. No actual power failure occurs at the
computer equipment itself and, as a result, the SPU continues to operate. However, the actual behavior of the
system will vary depending on how much of the system equipment is provided with UPS power.
In the “minimal” case, where only the SPU and any Remote Busses receive UPS power (and assuming that
disks are external to the SPU), the system is most likely to appear to be dormant (like a traditional battery
backup method system) because the system can not make progress once the disks lose power and spin down.
The system will simply enter its “idle loop”, waiting for disk I/O operations to complete, and that won't
happen until AC power returns and the disks spin up again.
But in expanded UPS coverage systems, where some or all of the disks receive UPS power, the system may
continue to run to some extent. Again, it depends on what resources the system needs to perform its
workload. Batch jobs that only need CPU, memory, and disk I/O can continue to run undisturbed. Processing
that requires tape or printer or terminal I/O will be blocked if those peripherals do not have UPS power.
UPS Monitor/iX issues a warning message to the system console to notify the operator that the particular
UPS (identified by its LDEV number) has reported to the system that its input AC power has failed. In
Example G-1, UPS Monitor/iX reports and power failure and a recovery shortly thereafter:
Example G-1 Sample Console Messages from UPS Monitor/iX
:showtime
FRI, AUG 13, 1993, 11:27 AM
:
:11:27/50/UPS LDEV 102 reports loss of AC input power. (UPSERR 0033)
**RECOVERY FROM POWER FAIL**
11:27/50/UPS LDEV 102 reports AC input power restored. (UPSWRN 0036)
:
UPS Monitor/iX also writes a system log file entry that denotes the input power loss to the UPS device. Read
“To enable logging of UPS activity” and “To review UPS activity recorded in the system log file,” later in this
chapter for more information.
System Behavior When AC Power Returns
The behavior of the system when AC input power returns to the UPS is very similar to that of the battery
backup method systems. One of two things will happen: a recovery from power failure (if AC power returns
before the UPS battery that backs up the SPU becomes exhausted) or a system crash.
If AC power returns before the UPS battery becomes exhausted (up to fifteen minutes when starting with
fully charged UPS batteries; less if the batteries were already partially discharged), then the system recovers
from the AC power failure and resumes normal operation. In this case, UPS Monitor/iX displays a message on
the system console, posts an entry in the system log files, and broadcasts the following message to all active
user terminals:
** RECOVERY FROM POWERFAIL **
If the UPS battery that powers the SPU becomes exhausted before AC input power returns, then the system
really does lose AC power and crashes. In this case, when AC power does return and the UPS turns on again,
the system reboots just as if it used battery backup.