Date: Sun, 25 May 2014 09:43:50 -0700 From: Nathan Whitehorn <nwhitehorn@freebsd.org> To: Allan Jude <allanjude@freebsd.org>, Kurt Lidl <lidl@pix.net> Cc: freebsd-sysinstall@freebsd.org, "Michael W. Lucas" <mwlucas@michaelwlucas.com> Subject: Re: bin/164281: bsdinstall(8): please allow sysinstall as installer option Message-ID: <53821DC6.60701@freebsd.org> In-Reply-To: <53821B1F.8000509@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>
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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
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