WhyAmIgettingMemoryErrors

To help understand why you are seeing memory errors, please have a look at HowMemoryEdacHardwareWorks.

You may well have been experiencing these errors for a while, it's just that nothing was checking them until you enabled the EDAC module. Note that your system is probably experiencing data corruption (if you are getting UEs - uncorrectable errors), so you should really check this out (this is why EDAC is set to `panic()` on UEs by default).

The reason that you are seeing problems is very likely to be one of:

• Your RAM is bad.
• Your Motherboard is bad.
• Your CPU is bad (for CPUs which have the memory controller built into the CPU core, such at the AMD Opteron/Athlon-64).
• The connection between your motherboard and your CPU, or memory module is bad.
• Some of your hardware is being operated outside of its design specification, such as:
  • Things are being run too hot.
  • Timings are being violated (e.g. running memory too fast, or bad DRAM clock generation).
  • Supply voltages to the critical compontents are too high/low (this may even happend very briefly, as a supply "spike", or "droop").
• You have seen one or more "Single Event Upsets" - see SoftErrors.
• Memory ECC check bits are not properly initialised by BIOS prior to Linux boot. See Uninitialized ECC bits
• The EDAC module is buggy.
• Memory loading is exceeded.
• The powersupply is insufficient.

So Which One Is It Then?

Good question. Time to try some things:

Symptoms

Here are the most likely symptoms.

Problem	Error Addresses	Error Slot or Row	Error Frequency
Bad Memory Module(s)	Single/Few	Probably only 1	May vary if part is marginally out of spec
Bad Motherboard	Probably many	Maybe 1, maybe many	?
Bad Connection	Probably many	1 (bad mem), prob all (bad CPU)	?
Temp out of spec	Probably few	Maybe one, if different mem mfrs/parts	Usually higher, with higher temp
Timings out of spec	Probably few	Maybe one, if different mem mfrs/parts	Usually higher, with higher temp
Voltages out of spec	Probably random	Maybe one, if different mem mfrs/parts	Usually higher at higher system load
Bad BIOS check bit init	Probably random	Probably all	High/very high (stops after a while for systems with background scrub)
Single event upsets	Random	Varies with effective "cross-section" of part	Rare - more common with some part designs, and at high altitude etc.

Things to try to isolate the problem

General:

• Get a second opinion e.g. from [[1]] or [[2]] - note that you should be sure that either:
  • The memory testing software knows how to disable ECC on your system, or
  • You have disabled ECC before running memory tester (note that memtest86 currently displays "ECC: No" on chipsets which have ECC, but which it doesn't know about!).
• This may not catch problems like power-supply related problems, which don't occur when the memory tester is running.
• Use a system stress tester such as "burnbx" from [[3]].
• Put your system under stress by (e.g.) running a parallelised Linux kernel build, whilst doing some heavy 3D graphics display, and a lot of disk I/O.

Suspected bad module:

• Remove Module.
• Move Module to different slot (do errors move with module).
• Move Module to different machine.
• See "suspected temp out of spec".
• See "suspected timings out of spec".
• See "voltages out of spec".
• Clean connections.
• Check Memory Loading
  • Some memory controllers can only support so many 'ranks' of memory at a given speed.

    For example, Opterons/Athlon64s can support only 4 ranks of 2 GB at PC3200. 
    See http://www.valueram.com/memoryranks/default.asp for definitions.

Suspected bad motherboard:

• Check motherboard docs for memory module compatability.
• Move modules to different slots.
• Clean connections.
• Upgrade BIOS.
• Select BIOS "fail-safe defaults", or equivalent change settings from there to isolate cause.

Suspected bad connection:

• Visually check connectors, pins, modules etc.
• HowToCleanEdgeConnectors.

Suspected temp out of spec:

• Measure temp, compare to published specs:
  • Use internal machine sensors (motherboard, hard drive etc.) if possible.
  • Use a temperature probe or infra-red thermometer.
• Check airflow.
• De-dust.
• Lower temp:
  • Lower room temp.
  • Increase cooling.
  • Improve airflow (tidy cables etc.).

Suspected timings out of spec:

• Try different BIOS version.
• Set pessimistic memory timings in BIOS.
• Compare memory controller timings to DIMM specs, using decode-dimms.pl from the Linux i2c project.
• Try disabling "spread spectrum" in the BIOS (easy if available), or by using an i2c driver for your board's clock generator (hard).

Suspected voltage out of spec:

• Check PSU specs vs. total demand of system components.
• Swap power supply with another machine.
• Fit voltage regulator/spike suppressor to machine power supply.

Suspected single event upsets:

• Fit less susceptible components
• Move to a lower altitude, or area with lower cosmic radiation.
• Move your data centre underground.
• Improve error-reporting utilities to ignore them.

Suspected bad check-bit init:

• Upgrade BIOS.
• Don't enable BIOS "quick boot".
• Don't manually skip BIOS memory check.

Suspected insufficient powersupply:

• Try detaching some devices that are hardly use. Start with USB devices.
• If the problems stop, either structurally reduce the devices, or get a higher capacity powersupply.
• Use a DC current clamp (pref one with peak/inrush measurement function) to check over-capacity at a particular voltage.
• This is closely related to voltage out of spec. That can also be caused by just a broken supply.