To prevent possible data loss due to electric power failure, each disk array and host are powered through ONLINE UPS. UPS = Uninterruptible Power Supply
To date, the main Terapix systems (that is CPUs, RAID arrays and disks) are powered by various Powerware online UPS, from Powerware company.
In case of electrical power failure, the batteries can continue to power all the devices for about 6 minutes, which is largely enough to complete a clean shutdown procedure. Then, the UPS power off the devices.
In case of electrical power failure, and if it last over 15 seconds, the computer starts a shutdown procedure.
Note also :
the UPS gives a regular filtered power, fairly constant in voltage and frequency, that make the devices to last longer.
in case of electrical power failure, the complete shutdown prevents "file system check" that could be tedious after a crash... Typically, it takes about half an hour to "fsck" a RAID volume after a crash.