User`s guide

System Troubleshooting and Diagnostics
5.2 Product Fault Management and Symptom-Directed Diagnosis
The kernel performs memory scrubbing of DRAM memory cells that
may flip due to transient alpha particles. Scrubbing simply reads the
corrected data and writes it back to the memory location. Returning
memory modules that only have SCRUBBED set in STATUS will cost
the corporation money, since the repair centers will generally not find a
problem.
Unlike uncorrectable ECC errors, the error handling code cannot indicate if
the page has been replaced. To get some idea, use DCL command, SHOW
MEMORY. If the page mapout threshold has not been reached ("PAGE
MAPOUT THRESHOLD EXCEEDED" is not set in SYSTAT packet header
register ( )), the system should be restarted at a convenient time to allow
the power-up self-test and ROM-based diagnostics to map out these pages.
This can be done by entering TEST 0 at the console prompt, running an
extended script TEST A9, or by powering down then powering up the
system. In all cases, the diagnostic code will mark the page bad for hard
single address errors, as well as any uncorrectable ECC error by default.
If there are many locations affected by hard single-cell errors, on the order
of one or more pages per MB of system memory, the memory module should
be replaced. The console command SHOW MEMORY will indicate the
number of bad pages per module. For example, if the system contains
64 MB of main memory and there are 64 or more bad pages, the affected
memory should be replaced.
Note
Under the OpenVMS operating system, the page mapout threshold
is calculated automatically. If "PAGE MAPOUT THRESHOLD
EXCEEDED" is set in SYSTAT ( ), the failing memory module should
be replaced.
In cases of a new memory module used for repair or as part of system
installation, one may elect to replace the module rather than having
diagnostics map them out, even if the threshold has not been reached for
hard single-address errors.
• MULTIPLE ADDRESSES ( )—If the second occurrence of an error within
a footprint is at a different address (LOWEST ADDRESS not equal to
HIGHEST ADDRESS ( ), MULTIPLE ADDRESSES will be set in STATUS
along with SCRUBBED. Scrubbing will not be attempted for this situation.
In most cases, the failing memory module should be replaced regardless of
the page mapout threshold.
System Troubleshooting and Diagnostics 5–23