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: >=20 > On 15 September 2015 at 22:52, Jim Thompson <jim@netgate.com = <mailto:jim@netgate.com>> wrote: >=20 > <snip> >=20 > 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. >=20 > <snip>=20 >=20 > 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=E2=80=99ll find that the default for =E2=80=98scrub=E2=80=99 = is off on most (perhaps all) boards. There are reasons, and these = relate directly to =E2=80=9Csignificantly diminish system = performance=E2=80=9D, (above), as well as the greatly increased RAM = sizes in use today. =E2=80=99Scrub' was popular about a decade ago, when DDR2 RAM was around = $100/GB. DDR3-1600 is about $6/GB today. Jim
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