SMIT offers a switch for ECC memory scrubbing, off or on.
The default is "off". I read about it in Info, and it sounds
like something I want to have enabled for availability and
integrity reasons. But if it is goodness, why is it's default
"off"? And if default is "off" , why turn it "on" at all?
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A: Memory scrubbing helps to prevent the RISC from encountering a
memory error from which it cannot recover. It checks for single bit
errors in a range of memory and corrects them before they possibly
degrade to double bit errors. Double bit errors in memory will cause
the system to halt.
If you turn memory scrubbing ON, there may be a slight performance
degradation (i.e. page faults) on the system. This is because
memscrub can force a process out to paging space (while the process
is sleeping). When the process becomes runnable, the context switch
occurs and the system will have to fault in the pages again because
memscrub was using the process' physical memory space. If memscrub
was not running, there could be a good chance the pages are still in
physical memory (this is depending on the load upon the system and
memory demands of course).
Memory scrubbing is by default turned OFF. One reason is that
there is no support for memory scrubbing on all machines, such as
the 220 (as the 220 hardware does not support EEC). Another reason
is performance. The default is OFF probably because faster
performance was considered a better "default setting" than improved
reliability. For example, it is best to run a benchmark is with
memscrub disabled. However, you can turn memory scrubbing ON or
OFF.
If you decide to turn memory scrubbing on, make sure that the
fixes to the following APARs have been applied before doing so:
o IX27144 -- fix is PTF U404117 (3240 PMP)
o IX29912 -- fix is PTF U411676 (3240 PMP)
Please call Software Services at 1-800-237-5511 to order the most
current PTF fixes for your particular AIX system level.
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This item was created from library item Q651003 1QGDG
Additional search words:
APPEARS ARISC CUSTORG INFO INFOEXPLORER IX JAN94 MAIN MEMORY OZIBM
OZNEW RISC SCRUBBING STORAGE TURN 1QGDG
WWQA: ITEM: RTA000037854 ITEM: RTA000037854
Dated: 11/1996 Category: RISCOHW
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