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DATE 2017-01-01

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MESSAGE
DATE 2017-01-19
FROM Rick Moen
SUBJECT Subject: [Learn] [Hangout-NYLXS] RAM and RAM-testing
From learn-bounces-at-nylxs.com Thu Jan 19 16:57:52 2017
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----- Forwarded message from Rick Moen -----

Date: Thu, 19 Jan 2017 13:02:03 -0800
From: Rick Moen
To: Ruben Safir
Subject: Re: (forw) [conspire] Old hardware, ridiculously old hardware:
free RAM for you

Quoting Ruben Safir (ruben-at-mrbrklyn.com):

> On 01/19/2017 02:46 AM, Rick Moen wrote:
> > through memtest86. Overnight, the machine hard-froze in that
> > RAM-checker, so hard that even the keyboard's NumLock key didn't even
> > toggle the LED.
>
> Oh god. It is painful to even think about running that test. I don't
> think there is a memtest86 for 64 bit systems. Suse stopped including
> it on disks because of some licensing issues with a new version.

I vaguely recall that there were at the time, and perhaps still are, two
different forks of the memtest86 codebase (maybe memtest86 and
memtest86+), and there were licensing issues with one but not the other.
The bigger problem though, in my opinion, is that it's just not good
enough! It finds gross errors but very often completely misses damage
bad enough to cause NMIs, segfaults, system freezes, and spontaneous
reboots. Whereas, parallel ('make -j N', for sufficiently large value of
N to exercise all of one's RAM) iterative kernel compiles are completely
successful -- in the sense that if you run them overnight and there's no
system freeze or short uptime, you know you do _not_ have bad RAM.

If you _did_ have a system freeze during the night, or have short
uptime, you now have a separate problem, that of isolating the problem
to the particular hardware component at fault. It could be a single RAM
stick. It could be multiple RAM sticks. It could be a motherboard
circuitry fault. It could be RAM sticks not properly lodged in their
sockets or corroded pins. It could even in theory be a marginal system
PSU, or maybe even a dodgy expansion board, a bad RAM socket, or such a
board not properly connecting in its socket. Isolating the root cause
requires using logic and part removal/substitution. For example, I
found the two bad 512MB ECC sticks by moving sticks to different sockets
(which ruled out bad sockets), and by running with some sticks removed
until I had a combination in which iterative parallel kernel compiles
could proceed without freezes or spontaneous reboots.

It surprised me that there were _two_ bad sticks of RAM. Ordinarily,
you would distrust a coincidence like that. However, I remembered that
I got them for free because they had probably been data center pulls:
Someone had probably yanked them from production servers because they
were both suspect, and it turns out that the suspicion was well-founded.
Fortunately, I still had the pair of 128MB ECC PC100 SDRAM sticks, and
bought a substitute pair of 512MB ECC PC100 SDRAM sticks immediately
after this testing. Throwing away what at the time was valuable RAM was
painful, but not as painful as an unstable server.

As it turns out, I really should have remembered, back then in 2006, to
look in the ECC event log, in the Intel L440GX+ 'Lancewood'
motherboard's BIOS: IIRC, it would have a lot more quickly told me
which stick in which RAM socket was having error problems. Part of my
point in my 2017 (current) posting is that looking in the Supermicro's
BIOS error log _did_ pinpoint the dodgy 4GB RAM stick -- after I
remembered the lessons of ten years ago.

All of these things are particularly important to understand for those
of us who accept donated hardware -- because often as not, the hardware
we receive was set aside because someone suspected there might be a
problem but lacked the time to do hardware diagnosis and find which
part is causing the problem and what to do about it.


----- End forwarded message -----
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