Date: Tue, 26 Aug 2025 15:31:44 +0200 From: =?UTF-8?Q?Aur=C3=A9lien_Couderc?= <aurelien.couderc2002@gmail.com> To: freebsd-hackers@freebsd.org Subject: Re: NFSv4.2 READ_PLUS support? Message-ID: <CA%2B1jF5qfMJAkGPL65a7sn0vZtpUjUZ1%2BQEy8eh=%2BUK33EhCAqg@mail.gmail.com> In-Reply-To: <861pozwrpo.fsf@ltc.des.dev> References: <CALXu0UfzyaZti2dSbZHPf_YXU88_2oCP98cXJPM6mQ9Fsr6ZuQ@mail.gmail.com> <CAM5tNy7x=AttZiu=ZLFtiQS3U2JD=gZOgjeGE-VoB1Obp9eZxQ@mail.gmail.com> <aKh3ZpxPYSIfMFfX@kib.kiev.ua> <CAM5tNy6WL93tVX18RsEUymYXON-W50i_-xm1CxrN6n0nbecmYg@mail.gmail.com> <CALXu0Uf%2B=GD8ZkZmN1v3s2GKp8Y5VDoiTO-cjay3Ypf1wmPMQw@mail.gmail.com> <eeb8551b-2f55-49c0-aabb-f68875495671@app.fastmail.com> <861pozwrpo.fsf@ltc.des.dev>
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On Mon, Aug 25, 2025 at 1:45 PM Dag-Erling Smørgrav <des@freebsd.org> wrote: > > "Rob Norris" <robn@despairlabs.com> writes: > > Cedric Blancher <cedric.blancher@gmail.com> writes: > > > Holes are not sequences of 0x00 bytes. Holes means "no data here". ZFS > > > compression should preserve the sparse information, otherwise you turn > > > ANY sequence of 0x00 bytes into holes,and that will break databases > > > and other applications which depend on exactly that *precise* > > > semantics. > > This is the second time I've heard this on this list (previously[1]) but > > I don't know what it's referring to. > > They made it up. Nobody made that up. It's reality, even defined by POSIX, IETF NFS and the UNIX greybeards, long ago > A hole is just an optimization, and it is 100% up to > the file system whether holes are created and where. Any application > that considers a hole to be semantically different from a sequence of > zeroes is broken. No, this is part of POSIX (e.g. https://pubs.opengroup.org/onlinepubs/9799919799/ ff), *AND* traditional UNIX filesystem behaviour. As pointed out, changing hold to 0x00 bytes is bad, as it breaks existing applications (usually databases and scientific applications), Aurélien -- Aurélien Couderc <aurelien.couderc2002@gmail.com> Big Data/Data mining expert, chess enthusiasthelp
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