User guide

Hard Drive Arrays E-13
The cells used in the array accelerator batteries are recharged via a “trickle”
charge applied while system power is present. If posted writes were stored in
the memory of the array accelerator and power loss occurs, power must be
reinstated within approximately four days or the data stored in the memory
will be lost. Note that this depends on the present condition of the array
accelerator batteries. If this risk is too great, you can disable the array
accelerator.
IMPORTANT: It is possible for the batteries to be depleted when you install a new array
controller. It can take up to 36 hours of system operation to charge the batteries fully. In
this case, only the Array Accelerator is affected; your system will continue to run without
interruption.
During Power-On Self-Test (POST), the array controller checks the batteries.
If the battery charge is low or depleted, the array accelerator is disabled until
the batteries reach 90 percent charge. The board continues to function
properly, but at a slightly lower performance, until the batteries reach
90 percent charge. At this point, the array accelerator is automatically enabled.
Concurrent I/O Request Servicing
The RA4000 Controller has the capability to service hundreds of I/O requests
at a time. For example, if you request data that resides on the first drive and
another user requests data that resides on the second drive, the controller can
deliver both pieces of information at once.
Optimized Request Management
Optimized request management, also known as elevator trend sorting, is
another performance enhancement feature provided by the array controller.
The controller receives and queues multiple data requests from the operating
system. The controller then rearranges the requests in an order that optimizes
performance.
Consider the following example. The RA4000 Controller receives a request
for a physical drive that is not currently active. The controller schedules the
request immediately ahead of previously received requests already queued to
other active drives within the array. This request management process operates
concurrently with drive operations. The benefits of optimized request
management increase as greater demands are made on the drive subsystem.