Date: Wed, 30 Aug 2017 22:57:39 +0100 From: Frank Leonhardt <frank2@fjl.co.uk> To: freebsd-questions@freebsd.org Subject: Re: help creating new gmirror > 2TB Message-ID: <26f5e88e-1ea7-6332-ca5e-f055cfbdd280@fjl.co.uk> In-Reply-To: <CAFsnNZLeuLYEJVozsoSvDtvgfMf4UueJhm37waOQ5_kyxs-rhg@mail.gmail.com> References: <CAFsnNZLeuLYEJVozsoSvDtvgfMf4UueJhm37waOQ5_kyxs-rhg@mail.gmail.com>
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On 29/08/2017 21:12, William Dudley wrote: > Hi, > > I want to create a simple mirror > 2TB on a FreeBSD 10.3 system. > > I have 2 identical 4TB disks. > > The examples in freebsd handbook "geom-mirror" pages show creation of a 2TB > mirror using > MBR partitioning, and that has an upper limit of 2TB. > > Some documentation says not to use GPT partitioning with gmirror because > both store their information in the last sector on the disk. > > I'm not expert enough to be able to solve this myself. > > How do I create a gmirror of 4TB size? > > I want to partition it into 4 slices after I create it, but think I can use > gpart to do that. > > Note: I'm not interested in using zfs unless there's no way to do this with > gmirror. > I read too many zfs failure stories on this mailing list to be comfortable > with zfs. I still get a bit worried about this, but I'm 99.9% sure you'll be okay with MBR assuming it's an AFD (4K sector drive). The bodge/workaround works. If it's SAS instead of SATA, all bets are off. Although I use ZFS a lot, I still prefer geom mirror for twin-disk systems. I feel a lot more comfortable booting from it in the event of a failure. ZFS has its good points, but so does UFS. Trying to get geom mirror to work with GPT as it stands just leads to pain. I've taken a look at the code with a view to fixing this is no one else does, but UFS is so un-cool in most circles and I don't fancy doing it alone in case I zap someone's data. it doesn't look that tricky to move the metadata somewhere else, and by checking for a GPT you can select between the old/new block. It's unexpected interactions I'm worried about. I think we're safe with MBR until we pass 16Tb. Regards, Frank.
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