Date: Wed, 31 May 2023 15:46:30 -0700 From: David Christensen <dpchrist@holgerdanske.com> To: questions@freebsd.org Subject: Re: read and write back full disk to trigger relocation Message-ID: <bc916e98-eee8-ccca-1423-6e6bf8bb55cb@holgerdanske.com> In-Reply-To: <504607037.200282.1685569498612@ichabod.co-bxl> References: <a111b6a7-0bf8-d3b9-9611-a7fbf36635b3@artem.ru> <1957739901.520492.1685310340560@ichabod.co-bxl> <0d0186c5-9542-1af3-2ce3-e28480b4b6d7@holgerdanske.com> <1961596841.3509648.1685359514813@fidget.co-bxl> <00671d49-83b1-26a0-4e28-47eb0d7cb95c@holgerdanske.com> <2025846914.656453.1685438293844@ichabod.co-bxl> <d5e6aa60-f42d-7fbb-32a4-c7fb450d3a71@holgerdanske.com> <343655931.86727.1685490563032@ichabod.co-bxl> <82a367dd-a32e-17c7-acf7-1f6992ff20af@holgerdanske.com> <504607037.200282.1685569498612@ichabod.co-bxl>
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On 5/31/23 14:44, Sysadmin Lists wrote: > David Christensen May 31, 2023, 12:30:43 AM >> On 5/30/23 16:49, Sysadmin Lists wrote: >>> David Christensen May 30, 2023, 4:16:09 PM >>>> I would say the experiment should be repeated on real HDD's, but how do >>>> I detect if identical data has being written to the platters? The HDD >>>> controller also has a cache and could optimize away such writes. >>> >>> Isn't that what dd is claiming authoritatively to be doing? Otherwise, putting >>> that example in the manpage is dangerous and can lead to unexpected data loss. >>> >>> I don't speak C++ very good, but here's the source: >>> https://github.com/coreutils/coreutils/blob/master/src/dd.c >> >> <snip> >> >> Looking at FreeBSD code will not provide information about the HDD >> controller hardware and firmware. > > You're still not getting it: *they* are the ones claiming to be effectively > writing out those blocks. It's up to them to validate that claim by accounting > for whatever HDD controller hardware and firmware are doing. > > There's no magic at play; either the source code proves their claims and > assumptions or it doesn't. > > Perhaps you can submit a bug report asking them to remove that example from the > manpage, with something like "you can't make that claim without knowing what > every HDD controller hardware and firmware are doing." Will be interested in their > response. If you feel the need to file a bug report, go for it. David
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