Date: Sun, 25 May 2014 09:54:04 -0700 From: Nathan Whitehorn <nwhitehorn@freebsd.org> To: Allan Jude <allanjude@freebsd.org>, freebsd-sysinstall@freebsd.org Subject: Re: bin/164281: bsdinstall(8): please allow sysinstall as installer option Message-ID: <5382202C.2010202@freebsd.org> In-Reply-To: <53821E75.10000@freebsd.org> References: <201404151630.s3FGU0Zg026166@freefall.freebsd.org> <CAM9wqY8Bn9yQvMbpMdg1wcVhx5AGgK6rP1tkh9qccDhWZaU9Kw@mail.gmail.com> <012501cf5f1f$c5e7c740$51b755c0$@FreeBSD.org> <5358223B.1090408@gmail.com> <535827AC.3040503@allanjude.com> <53582CC4.2080808@freebsd.org> <53583D5C.5020506@pix.net> <53583DB8.1080905@freebsd.org> <20140423230210.GA20429@pix.net> <538219DA.3040702@freebsd.org> <53821B1F.8000509@freebsd.org> <53821DC6.60701@freebsd.org> <53821E75.10000@freebsd.org>
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On 05/25/14 09:46, Allan Jude wrote: > On 2014-05-25 12:43, Nathan Whitehorn wrote: >> On 05/25/14 09:32, Allan Jude wrote: >>> On 2014-05-25 12:27, Nathan Whitehorn wrote: >>>> I'm (finally) integrating these patches now. Could you remind me what >>>> the point of the gnop is? I'm not sure I get it. >>>> -Nathan >>> The 'gnop -S 4096 <device>' makes a virtual device that has a sector >>> size of 4096 bytes. This causes ZFS to set ashift=12 even for devices >>> that mis-advertise (lie about) their sector size. There is no real harm >>> in using 4k sectors on a 512b sector device, but using 512b sectors on a >>> 4k device will cause write amplification (read-modify-write) since the >>> device will have to deal with it as a partial block update. >> I think our ATA code mostly has this under control at this point. >> >>> Additionally, the sector size can only be set at pool creation time, >>> even if you have have 512b sector devices, you'll want to create your >>> pool as 4k, so that in the future when you add additional devices, or >>> replace failed devices, the 4k sector devices will be supported. ZFS >>> complains loudly when you try to add mis-matched sector size devices to >>> a pool. >>> >>> >> This is a good reason, even if the circumstances behind it are stupid. >> Is there really no way to handle this besides gnop? Can't we just fix ZFS? >> -Nathan >> _______________________________________________ >> freebsd-sysinstall@freebsd.org mailing list >> http://lists.freebsd.org/mailman/listinfo/freebsd-sysinstall >> To unsubscribe, send any mail to >> "freebsd-sysinstall-unsubscribe@freebsd.org" > Linux added an explicit option to the zpool, so you can just do: > > zpool create -o ashift=12 mypool mirror disk1 disk2 > > There was some discussion about this in the OpenZFS group, but it was > usually cited as a reason why there was a need to for OpenZFS, to keep > the Linux version from diverging and adding a bunch of non-standard options. > > I am not sure what the best option is. The gnop is only required while > the pool is being created, it doesn't need to be re-created in order to > import the pool etc, it is just to trick ZFS the first time. > If it's really just needed at creation time, the best way forward seems pretty clearly to be the -o ashift one. Let's see if we can do that. -Nathan
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