Date: Tue, 08 Oct 2013 22:41:30 +0200 From: Nathan Whitehorn <nwhitehorn@freebsd.org> To: Freddie Cash <fjwcash@gmail.com> Cc: FreeBSD-Current <freebsd-current@freebsd.org>, Allan Jude <freebsd@allanjude.com> Subject: Re: [CFT] Patch to bsdinstall to support root-on-ZFS and GELI Message-ID: <52546DFA.4000500@freebsd.org> In-Reply-To: <CAOjFWZ4BMMna25KnD7RgRiLr5dszjrT9AdGjJi5XQXB9q1=Tmw@mail.gmail.com> References: <52531295.7090700@allanjude.com> <52546844.2010608@freebsd.org> <CAOjFWZ4BMMna25KnD7RgRiLr5dszjrT9AdGjJi5XQXB9q1=Tmw@mail.gmail.com>
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On 10/08/13 22:25, Freddie Cash wrote: > On Tue, Oct 8, 2013 at 1:17 PM, Nathan Whitehorn > <nwhitehorn@freebsd.org <mailto:nwhitehorn@freebsd.org>>wrote: > > 4. What is this gnop stuff for? > > > Can't comment on the rest, but gnop is required to create 4K-aligned > vdevs where the minimum block size is 4K (aka ashift=12). Without > this, ZFS relies on the underlying disk driver providing the correct > information, and most don't. Also, if you don't do this, and create a > vdev using 512B sectors, the ashift will be set to 9, and replacing > the drive down the line with 4K Advanced Format drive will drop your > drive performance in the toilet. > > Thus, to future-proof your pool, you need to: > - set the ashift of the pool to 12 (4 KB) > - align the disk/partition on 4 KB boundaries (starting partition at > 1 MB works well) > > Until our ZFS gains the ability to set a minimum ashift for the pool, > or to set the ashift at vdev creation, or all drive manufacturers > write perfect firmware, than we need to fake it with gnop. > Well, that's a disgusting hack, but I see why it's there. Thanks for the explanation! -Nathan
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