Date: Tue, 15 Sep 2015 17:34:44 -0500 From: Jim Thompson <jim@netgate.com> To: Igor Mozolevsky <igor@hybrid-lab.co.uk> Cc: Dieter BSD <dieterbsd@gmail.com>, Hackers freeBSD <freebsd-hackers@freebsd.org>, freebsd-hardware@freebsd.org Subject: Re: ECC support Message-ID: <8435FBF3-2F8E-4A25-ABEA-B7038AFFE372@netgate.com> In-Reply-To: <CADWvR2h4XdYfy3i6zjLqC04uqihNwL9QtTgGN%2BZ8QbAkh9=%2BZA@mail.gmail.com> References: <CAA3ZYrBXZn1WpHWYGJYWJDPsk7iDahCas8RhnHC4w%2Babf4w4hA@mail.gmail.com> <41EFCF21-D3B0-4EC4-8EAB-417CA33821FC@netgate.com> <CADWvR2h4XdYfy3i6zjLqC04uqihNwL9QtTgGN%2BZ8QbAkh9=%2BZA@mail.gmail.com>
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> 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. ’Scrub' was popular about a decade ago, when DDR2 RAM was around $100/GB. DDR3-1600 is about $6/GB today. Jimhelp
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