Date: Sat, 8 Feb 2014 08:28:31 -0800 From: Freddie Cash <fjwcash@gmail.com> To: Johan Hendriks <joh.hendriks@gmail.com> Cc: FreeBSD Filesystems <freebsd-fs@freebsd.org> Subject: Re: Using the *real* sector/block size of a mass storage device for ZFS Message-ID: <CAOjFWZ7xCRwwrJcLyNy3%2Bt7zkevEK_r51pP70-xocpYmY3XT7w@mail.gmail.com> In-Reply-To: <CAOaKuAXwaUwKH0UDd2tA5G23KMwxR4%2BnLcU-0Xanm-qozKXkPg@mail.gmail.com> References: <1487AF77-7731-4AF8-8E44-FF814BB8A717@ebureau.com> <1391808195.4799.80708189.5CAD8A4E@webmail.messagingengine.com> <8B5D8D0C-ADDE-49B3-87A9-DE1105E32BF9@ebureau.com> <878utmxtum.wl%berend@pobox.com> <CAOaKuAXwaUwKH0UDd2tA5G23KMwxR4%2BnLcU-0Xanm-qozKXkPg@mail.gmail.com>
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On Feb 8, 2014 2:03 AM, "Johan Hendriks" <joh.hendriks@gmail.com> wrote: > > Op zaterdag 8 februari 2014 heeft Berend de Boer <berend@pobox.com> het > volgende geschreven: > > > >>>>> "Dustin" == Dustin Wenz <dustinwenz@ebureau.com <javascript:;>> > > writes: > > > > Dustin> Am I correct in assuming that it is absolutely impossible > > Dustin> to convert an existing ashift:9 vdev to ashift:12? Some of > > Dustin> my pools are approaching 1PB in size; transferring the > > Dustin> data off and back again would be inconvenient. > > > > I thought you could do it one disk at a time (if you have a redundant > > pool). > > > > But maybe not. > > > > -- > > All the best, > > > > Berend de Boer > > > No that is not possible. > The ashift is set when the pool is created, hence the fact that you only > need the gnop method at pool creation time. If you add a vdev to the pool > you do not need the gnop method anymore because you can not change it. > You can align the disk so it has a 4 k alignement. But that is not the > ashift of the pool Correction: the ashift is set at the vdev level, when the vdev is created. You only need to use the gnop method on a single disk in a vdev as zfs uses the largest ashift of all drives in the vdev. And you need to do it anytime you add a new vdev to a pool. I believe there's a sysctl in FreeBSD 10 where you can set the minimum ashift level so you don't need to use the gnop method.
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