D-14
Understanding Drive Arrays
Writer: Pamela King Project: SMART-2DH Array Controller Reference Guide Comments: 295469-002
File Name: K-APPD.DOC Last Saved On: 2/27/98 12:06 PM
COMPAQ CONFIDENTIAL - NEED TO KNOW REQUIRED
ECC Memory
To assure further data integrity, the Array Accelerator cache is made up of
ECC memory. ECC (Error Checking and Correcting) memory will detect and
correct all single-bit memory errors in multiple DRAMs. It will also detect all
two-bit memory errors in any position and most three- and four-bit memory
errors in a single DRAM. An entire DRAM can also fail without data loss.
This ensures the correction of common memory errors without interrupting
system operation.
Batteries
The Array Accelerator contains batteries that maintain any data cached there
if a system power failure occurs. The batteries can preserve data in the Array
Accelerator for up to four days. When power is restored to the system, an
initialization feature writes the preserved data to the disk drives.
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, you must
reinstate power 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 you feel 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 SMART-2DH 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 SMART-2DH Controller checks the
batteries. If the battery charge is low or depleted, a 1794 POST error message
is displayed indicating that the Array Accelerator is disabled. The controller
temporarily disables the Array Accelerator until the batteries reach 90 percent
charge. The board continues to function properly, at a slightly lower
performance, until the batteries reach 90 percent charge. At this point, the
Array Accelerator is automatically enabled.
