Date: Tue, 15 Sep 2015 18:23:39 -0700 (PDT) From: Don Lewis <truckman@FreeBSD.org> To: jim@netgate.com Cc: igor@hybrid-lab.co.uk, freebsd-hackers@freebsd.org, dieterbsd@gmail.com, freebsd-hardware@freebsd.org Subject: Re: ECC support Message-ID: <201509160123.t8G1NdvM023263@gw.catspoiler.org> In-Reply-To: <8435FBF3-2F8E-4A25-ABEA-B7038AFFE372@netgate.com>
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On 15 Sep, Jim Thompson wrote: > >> On Sep 15, 2015, at 5:19 PM, Igor Mozolevsky <igor@hybrid-lab.co.uk> >> wrote: >> >> On 15 September 2015 at 22:52, Jim Thompson <jim@netgate.com >> <mailto:jim@netgate.com>> wrote: >> >> <snip> >> >> Errors are corrected "on-the-fly," corrected data is almost never >> placed back in memory. If the same corrupt data is read again, the >> correction process is repeated. Replacing the data in memory would >> require processing overhead that could accumulate and significantly >> diminish system performance. If the error occurred because of random >> events and isn't a defect in the memory, the memory address will be >> cleaned of the error when the data is overwritten with other data. >> >> <snip> >> >> Just to correct a small oversight- most (if not all?) boards have an >> option to scrub ECC memory in the background so as to prevent single >> bit (recoverable) errors from turning into double bit (irrecoverable >> but detectable) errors ;-) > > I think you’ll find that the default for ‘scrub’ is off on most > (perhaps all) boards. There are reasons, and these relate directly to > “significantly diminish system performance”, (above), as well as the > greatly increased RAM sizes in use today. The Gigabyte AM3+ motherboards that I'm using have all sorts of knobs for controlling the scrub rate, with different knobs for cache scrubbing vs. main memory scrubbing. My somewhat more recent Asus AM3+ board with different BIOS brand basically just has an ECC on/off knob.
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