IBM DS4800 User, Installation And Maintenance Manual page 39

Attention: Because the interconnect-battery unit provides electrical signal
connections between the controllers, removing the interconnect-battery unit
interrupts the communications between the controller units in the DS4800, resulting
in a loss of communication between controllers A and B. Data access is limited to
only controller A when the interconnect-battery unit is removed. Controller B is in an
off-line state while controller A performs all controller operations. To prevent any
problems as a result of this condition, controller B must be placed off-line before
you remove the interconnect-battery unit. See "Replacing the interconnect-battery
unit" on page 148 for more information. Failure to observe the instructions and
prerequisites described in "Replacing the interconnect-battery unit" on page 148
might result in a loss of data access.
Figure 7 shows how the interconnect-battery unit slides into the front of the storage
subsystem. The levers securing the interconnect-battery units to the storage
subsystem are shown in the released position.
Interconnect-
battery unit
Levers
in released
position
Figure 7. Interconnect-battery unit
The interconnect-battery unit contains two battery packs that provide backup power
to the controller cache memory. Each battery pack contains sealed, rechargeable
lithium ion batteries. The battery packs can maintain data in the cache for at least
three days.
The battery chargers in the power supply-fans perform a battery test when the
storage subsystem is started and on a regularly scheduled interval thereafter. Data
caching is suspended during periods when the controllers performed battery tests.
The interconnect-battery unit is hot-swappable. You can remove the
interconnect-battery unit for servicing and then reinsert it while the DS4800
continues to perform I/O operations.
17
Chapter 1. Introduction