Date: Mon, 28 Jan 2013 11:03:05 +0000 From: Steve O'Hara-Smith <ateve@sohara.org> To: Volodymyr Kostyrko <c.kworr@gmail.com> Cc: freebsd-questions@freebsd.org Subject: Re: ZFS - whole disk or partition or BSD slice? Message-ID: <20130128110305.779e82e5c2c060be317216b6@sohara.org> In-Reply-To: <510647A5.2060804@gmail.com> References: <5105BEE4.4030402@mansionfamily.plus.com> <5105D611.4000506@ShaneWare.Biz> <CAHu1Y73i0645eP_M1fogOtUAuVw-Fb4c7f%2B-rFX%2B6z7-4ea9nw@mail.gmail.com> <20130128070324.08bc4d67f570835d75d90497@sohara.org> <510647A5.2060804@gmail.com>
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On Mon, 28 Jan 2013 11:40:53 +0200 Volodymyr Kostyrko <c.kworr@gmail.com> wrote: > 28.01.2013 09:03, Steve O'Hara-Smith: > > On Sun, 27 Jan 2013 22:05:05 -0800 > > Michael Sierchio <kudzu@tenebras.com> wrote: > > > >> On Sun, Jan 27, 2013 at 5:36 PM, Shane Ambler <FreeBSD@shaneware.biz> > >> wrote: > >> > >>> I recall reading that using partitions for zfs on FreeBSD was as good > >>> as full disks. > >> > >> No, it isn't - ZFS can fully utilize disk caches when presented with > >> whole devices. There are possible reasons to create partitions - one > >> being that if an unfriendly OS sees the device, it won't try to > >> initialize it if it sees a partition map. Another is using a cheap > >> RAID controller that can't be fully disabled - in which case you > >> generally need to create a partition that doesn't include the last few > >> sectors of the disk, where such controllers keep magic data. > > > > There's one other good reason to use partitions when mirroring. > > When the time comes to replace a drive in a mirror it is necessary that > > the new drive be the same size (or larger) than the one it replaces. > > Given that drives of nominally the same capacity (and even of the same > > type and brand bought at different times) tend not to be exactly the > > same size using a partition a little smaller than the whole drive makes > > it certain that a replacement drive will be big enough to use in the > > mirror when it arrives. > > There's no need for that as ZFS can use same or bigger partition to > mirror existing one. If the second one would be smaller - do some math > and cut out some swap space. The problem arises when a drive fails, you order a replacement (go down the shop whatever) and when the new disc arrives and it's a few blocks smaller than the existing one. Then it cannot be used to mirror the existing one and you're in for a messy job to get a working mirror up. -- Steve O'Hara-Smith <steve@sohara.org>
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