help creating new gmirror > 2TB

Mikhail Goriachev mikhailg at
Wed Aug 30 14:56:53 UTC 2017

On 29/08/2017 17:12, 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.
> Thanks in advance,
> Bill Dudley

Hi Bill,

Great articles that helped me a lot back awhile:

In regard with disk thrashing, just mirror one essential partition. IMO
thrashing isn't that bad if it happens once or twice a year... but it
takes a long time and the disks go nuts. GPT is the way to go in your


Mikhail Goriachev

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