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Old 12-08-2007, 02:33 AM
"Roopnarine, Peter"
 
Default Is ECC memory any use?

First, apologies for the top posting. On the road, and using my company's
stinky MS webmail.
But, ECC memory is absolutely a good idea if you're performing a lot of
RAM-intensive operations, such as in numerical simulations and so on. Error
occurrences are infrequent, but of course will increase in frequency as
memory access, and the amount of memory in the system(!) increases. So if
you're at all involved in that sort of work, then ECC is worth the minimal
effort of use.
Peter

Peter D. Roopnarine, Assoc. Curator
Dept. of Invertebrate Zoology & Geology
California Academy of Sciences
875 Howard St.
San Francisco CA 94103
USA

http://zeus.calacademy.org/roopnarine/peter.html
http://www.calacademy.org/blogs
Tel. (415)321-8271
FAX (415)321-8615
Climate change begins and ends at home



-----Original Message-----
From: fedora-list-bounces@redhat.com on behalf of Timothy Murphy
Sent: Fri 12/7/2007 5:07 PM
To: fedora-list@redhat.com
Subject: Is ECC memory any use?


I'm getting memory for a very old (P2B-LS) Asus motherboard,
and I see I can get ECC memory for some 20% more.

Is there any point in getting this?
I see there is quite a lot of work
in getting ECC testing incorporated into the Linux kernel.
But even if it were there, would it be very valuable?

I have a feeling that disk errors are far more likely
than RAM errors.
Is that right?


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Old 12-08-2007, 06:32 AM
John Summerfield
 
Default Is ECC memory any use?

Timothy Murphy wrote:

I'm getting memory for a very old (P2B-LS) Asus motherboard,
and I see I can get ECC memory for some 20% more.

Is there any point in getting this?
I see there is quite a lot of work
in getting ECC testing incorporated into the Linux kernel.
But even if it were there, would it be very valuable?


Whether to use ECC ram depends on the mobo; some support it, some don't.

I suspect that mobo supports 384 Mbytes of SDRAM, probably no faster
than PC-100 (but PC-133 works fine); it might not even require it that fast.


I've just been to a computer auction; I suspect that wouldn't even
attract a bid. I'm not sure that there was anything less than a 1.7 Ghz PIV.

<checks>
There were two COMPAQ DESKPRO Pentium IIIs, they went for $AU60+10%
buyers' premium +10% GST.



It would make a fine firewall (and until recently I was using a Pentium
II for just that), but _I_ wouldn't be spending money on it.


The question isn't so much whether it can do a useful job, as for how
long it will do so.


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John

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Old 12-08-2007, 07:44 AM
"Mike Fleetwood"
 
Default Is ECC memory any use?

On 08/12/2007, Timothy Murphy wrote:
> I'm getting memory for a very old (P2B-LS) Asus motherboard,
> and I see I can get ECC memory for some 20% more.
>
> Is there any point in getting this?
> I see there is quite a lot of work
> in getting ECC testing incorporated into the Linux kernel.
> But even if it were there, would it be very valuable?
>
> I have a feeling that disk errors are far more likely
> than RAM errors.
> Is that right?

I would personally always use ECC memory. Here's D. J. Bernstein's
recommendation on the subject: http://cr.yp.to/hardware/ecc.html

ECC detection and correction usually has to be enabled in the BIOS and
is performed by the hardware. Linux kernel from 2.6.16 includes the
EDAC project (http://bluesmoke.sourceforge.net/) code to report memory
errors and corrections to syslog for supported motherboard chip sets.
Also see Documentation/drivers/edac/edac.txt in the Linux kernel
source tree.

Thanks,
Mike

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Old 12-08-2007, 11:29 AM
Bruno Wolff III
 
Default Is ECC memory any use?

On Sat, Dec 08, 2007 at 01:42:29 +0000,
Alan Cox <alan@lxorguk.ukuu.org.uk> wrote:
>
> If you are doing complex scientific processing or banking where an error
> isn't acceptable then its essential. If you can tolerate the small change
> of a bit flip ever year or two then its far less of a concern.

I sat in on a discission with the group doing analysis of LIGO data at our
University and while they were doing scientific work, they concluded that
they didn't need to use ECC memory because the odds of a false negative
were acceptibly low and for false positives they could just rerun the test.
This is from the same people that found the error correction in TCP/IP not
to be sufficent and worried about how to check the files and to be able to
reacquire reason parts of the files as they were large enough that resending
whole files after a checksum failure was not ideal. So just because the
use is scientific, buying ECC memory may not be the most economical solution
to the problem.

P.S. Sorry about the duplicates. I forgot to delete the message from my
outbound email queue after waiting for the first copy to be sent. I still
haven't heard back on my infrastructure ticket complaning about getting
deferral status back for messages that seemed to be getting accepted for
delivery to redhat's list server for the last 2 weeks.

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Old 12-08-2007, 06:57 PM
Timothy Murphy
 
Default Is ECC memory any use?

John Summerfield wrote:

>> I'm getting memory for a very old (P2B-LS) Asus motherboard,
>> and I see I can get ECC memory for some 20% more.
>>
>> Is there any point in getting this?
>> I see there is quite a lot of work
>> in getting ECC testing incorporated into the Linux kernel.
>> But even if it were there, would it be very valuable?
>
> Whether to use ECC ram depends on the mobo; some support it, some don't.
>
> I suspect that mobo supports 384 Mbytes of SDRAM, probably no faster
> than PC-100 (but PC-133 works fine); it might not even require it that
> fast.

Actually this 450MHz PIII motherboard supports 1GB of ECC PC100 RAM.

> I've just been to a computer auction; I suspect that wouldn't even
> attract a bid. I'm not sure that there was anything less than a 1.7 Ghz
> PIV. <checks>
> There were two COMPAQ DESKPRO Pentium IIIs, they went for $AU60+10%
> buyers' premium +10% GST.

Well, I'm not planning on selling this machine.
But your comment does raise a point I've often wondered about -
is CPU speed really that important, if one is not a gamer or similar?

This machine is actually only used as a server,
serving (externally) httpd, mysql, php and openldap.
As far as I can see, the slow CPU speed of the machine
has never had the slightest deleterious effect.
The bottleneck in all cases has been the speed of my ADSL connection
(4Mb/s download, according to my ISP, but under 2Mb/s in practice).

So I do genuinely wonder - does CPU speed matter at all, in such a case?

This Asus motherboard has been remarkably resilient
during its long (9 1/2 years) life.
The CMOS battery expired (and was replaced) about 3 years ago;
and two SCSI disks have gently ended their lives,
in each case giving me due warning of their coming demise.

> The question isn't so much whether it can do a useful job, as for how
> long it will do so.

I have often thought of replacing it, as I said.
But is there any real reason to do so?


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Old 12-08-2007, 07:28 PM
John Summerfield
 
Default Is ECC memory any use?

Timothy Murphy wrote:

John Summerfield wrote:


I'm getting memory for a very old (P2B-LS) Asus motherboard,
and I see I can get ECC memory for some 20% more.

Is there any point in getting this?
I see there is quite a lot of work
in getting ECC testing incorporated into the Linux kernel.
But even if it were there, would it be very valuable?

Whether to use ECC ram depends on the mobo; some support it, some don't.

I suspect that mobo supports 384 Mbytes of SDRAM, probably no faster
than PC-100 (but PC-133 works fine); it might not even require it that
fast.


Actually this 450MHz PIII motherboard supports 1GB of ECC PC100 RAM.


I had a p2l (LX chipset) board back when PII was new. Memory is fading
into the mists of tine:-(







I've just been to a computer auction; I suspect that wouldn't even
attract a bid. I'm not sure that there was anything less than a 1.7 Ghz
PIV. <checks>
There were two COMPAQ DESKPRO Pentium IIIs, they went for $AU60+10%
buyers' premium +10% GST.


Well, I'm not planning on selling this machine.


I was targeting its value in terms of replacement cost; a cheapish used
Pentium IV has more life expectancy than an aged Pentium II (or III).
That and whether it's sensible to throw more money at such a dated box;




But your comment does raise a point I've often wondered about -
is CPU speed really that important, if one is not a gamer or similar?

This machine is actually only used as a server,
serving (externally) httpd, mysql, php and openldap.
As far as I can see, the slow CPU speed of the machine
has never had the slightest deleterious effect.
The bottleneck in all cases has been the speed of my ADSL connection
(4Mb/s download, according to my ISP, but under 2Mb/s in practice).

So I do genuinely wonder - does CPU speed matter at all, in such a case?


No, but reliability might. If you chose to serve stuff internally, a
faster disk drive (up to 60 Mbytes/sec) might interest you:-) It won't
go anything like that fast in that box, and I'm not sure whether an
LBA48 drive would work with it. A small one probably would.


fwiw it's most likely to fail after a period of being turned off.


If you don't have a performance problem, adding RAM won't help.
If you do, faster everything probably will, without much thought beyond
brand and budget.


You didn't say how much RAM; it would be interesting to price it and
compare with a low-end server from HP, Dell & Lenovo/IBM (or anyone
else). the low-end server may come with guarantee and on-site support.
New features such as virtualisation may be attractive too.




This Asus motherboard has been remarkably resilient
during its long (9 1/2 years) life.

The CMOS battery expired (and was replaced) about 3 years ago;
and two SCSI disks have gently ended their lives,
in each case giving me due warning of their coming demise.


The question isn't so much whether it can do a useful job, as for how
long it will do so.


I have often thought of replacing it, as I said.
But is there any real reason to do so?


Depends on the uncertain (and unplanned) time if its demise and the
certain (and planned) time of its replacement.


I took a couple of weeks recently visiting daughters in Victoria, and at
the end of the first week there was a power failure here, and part of my
network didn't come back up. Not being able to connect to my desktop was
inconvenient.


When I got back I found the smoke had escaped from a switch and my
office ponged seriously for weeks after.


Whether a newer switch (it was a moderately serous rack-mount affair)
would have survived is moot, but having older gear is a bigger
invitation to such inconveniences.


--

Cheers
John

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Old 12-09-2007, 08:45 AM
Chris Snook
 
Default Is ECC memory any use?

Timothy Murphy wrote:

I'm getting memory for a very old (P2B-LS) Asus motherboard,
and I see I can get ECC memory for some 20% more.

Is there any point in getting this?
I see there is quite a lot of work
in getting ECC testing incorporated into the Linux kernel.
But even if it were there, would it be very valuable?

I have a feeling that disk errors are far more likely
than RAM errors.
Is that right?




Depends who's buying. Few people do anything on "personal" systems that really
justifies ECC RAM, though I'm sure the exceptions are probably on this list. If
you're doing any kind of business work where uptime is important, or any kind of
technical work where bit flips could cause nasty side effects, it's probably
worth buying the ECC, unless you're doing high-end graphics where a stray pixel
won't make a difference and most of your power budget is going to the GPUs.


-- Chris

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Old 12-09-2007, 04:57 PM
Timothy Murphy
 
Default Is ECC memory any use?

Chris Snook wrote:

>> I'm getting memory for a very old (P2B-LS) Asus motherboard,
>> and I see I can get ECC memory for some 20% more.
>>
>> Is there any point in getting this?

> Depends who's buying. Few people do anything on "personal" systems that
> really
> justifies ECC RAM, though I'm sure the exceptions are probably on this
> list.

I decided in the end to go with ECC,
even though as you say it is probably completely unnecessary in my case.
But the cost difference was negligible - $10 on 512MB, so I went for it.


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Old 12-10-2007, 07:49 AM
Les
 
Default Is ECC memory any use?

On Sun, 2007-12-09 at 04:45 -0500, Chris Snook wrote:
> Timothy Murphy wrote:
> > I'm getting memory for a very old (P2B-LS) Asus motherboard,
> > and I see I can get ECC memory for some 20% more.
> >
> > Is there any point in getting this?
> > I see there is quite a lot of work
> > in getting ECC testing incorporated into the Linux kernel.
> > But even if it were there, would it be very valuable?
> >
> > I have a feeling that disk errors are far more likely
> > than RAM errors.
> > Is that right?
> >
> >
>
> Depends who's buying. Few people do anything on "personal" systems that really
> justifies ECC RAM, though I'm sure the exceptions are probably on this list. If
> you're doing any kind of business work where uptime is important, or any kind of
> technical work where bit flips could cause nasty side effects, it's probably
> worth buying the ECC, unless you're doing high-end graphics where a stray pixel
> won't make a difference and most of your power budget is going to the GPUs.
>
> -- Chris
>
You are assuming that only data resides in the memory, which is not the
case. Your program will act quite strangely if bits flip as well. ECC
has been dropped by some manufacturers because it is cheaper. Some
other forms of systems have an alternative scheme, but I prefer ECC.
That said, my current system doesn't have it because I misread the spec.
Bits do not typically "flip occasionally". As memory ages, a "feature"
of CMOS is something that creates bridges internal to the silicon. This
in turn causes failures. If you are lucky, the bit that fails will
match what is written to it. In which case no failure shows up. On the
other hand a bit that has a bridge can change state, and if you wrote a
0 to a bit that would bridge to a 1, then you will find that a program
can run for a while, then FLIP! and it doesn't work. You will get an
error message that will probably not say anything about a bit flipping,
and worse, it will not be repeatable because programs are dynamically
loaded, data is paged in and out, and memory is occasionally shifted
(depending on the OS means of optimizing memory access, and the language
or OS means of garbage collection). ECC memory means your programs will
work because your system can recover from these "single bit errors".
Note that very few ECC systems will correct multibit errors.

If you have too many failures in code running, with strange and non
repeatable conditions, you should begin to suspect memory errors,
whether or not you have ECC memory.

Regards,
Les Howell

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Old 12-10-2007, 01:52 PM
Bruno Wolff III
 
Default Is ECC memory any use?

On Mon, Dec 10, 2007 at 00:49:25 -0800,
Les <hlhowell@pacbell.net> wrote:
> Bits do not typically "flip occasionally". As memory ages, a "feature"
> of CMOS is something that creates bridges internal to the silicon. This
> in turn causes failures. If you are lucky, the bit that fails will

Bit flips are also caused by cosmic rays and those do happen occassionally.

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