Dell PowerVault 211S (SCSI) - Manual (Page 121)

support.dell.com Maintaining Your Storage System B-7
If a blackout occurs—even a temporary one—while the storage system is turned on,
turn off the storage system immediately and disconnect it from its power source.
Leaving the storage system turned on may cause problems when the power is
restored; other appliances left on in the area can create large voltage spikes that can
damage the storage system.
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A number of devices are available that protect against power problems, such as
power surges, transients, and power failures. The following subsections describe
some of these devices.
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Surge protectors are available in a variety of types and usually provide a level of pro-
tection commensurate with the cost of the device. Surge protectors prevent voltage
spikes, such as those caused during an electrical storm, from entering a storage sys-
tem through the electrical outlet. Surge protectors, however, do not offer protection
against brownouts, which occur when the voltage drops more than 20 percent below
the normal AC line voltage.
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Line conditioners go beyond the overvoltage protection of surge protectors. Line con-
ditioners keep the voltage supplied by the electrical outlet at a fairly constant level
and, therefore, can handle brownouts. Because of this added protection, line condi-
tioners cost more than surge protectors—up to several hundred dollars. However,
these devices cannot protect against a complete loss of power.
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A UPS offers the most complete protection against variations in power because it
uses battery power to keep the storage system running when AC power is lost. The
battery is charged by the AC power while it is available, so once AC power is lost, the
battery can provide power to the storage system for a limited amount of time—from
15 minutes to an hour or so—depending on the UPS system.
UPS systems range in price from a few hundred dollars to several thousand dollars,
with the more expensive units allowing you to run larger computer systems for a
longer period of time when AC power is lost. UPS systems that provide only 5 min-
utes of battery power let you conduct an orderly shutdown of the storage system, but
are not intended to provide continued operation.
If you are using the optional redundant power supplies installed in your storage sys-
tem, connect the two power supplies to different circuits, if possible.