gmirror, gpart and MBR vs GPT in the Handbook

Polytropon freebsd at
Mon Dec 2 17:26:47 UTC 2013

On Mon, 02 Dec 2013 12:13:32 -0500, Mike. wrote:
> My understanding is that MBR can be used with drives only up to
> and including 2TB in size.  So if I use MBR, the maximum drive
> size I could use would be 2TB.  Is that correct?

Don't confuse partitioning schemes and file systems. Both are
different things, happening on different "layers". To make it
simpler than it probably is:

Partitioning =
	a) MBR with classic tools (fdisk, bsdlabel)
	b) MBR with modern tool (gpart)
	c) GPT (gpart)
	d) Dedicated (only the "bsdlabel part")

RAID concepts =
	a) mirror
	b) stripe
	c) combined and extended forms ...

File system =
	a) UFS
		option +U: soft updates
		option +J: journal
	b) ZFS

Of course ZFS can handle things like "RAID concepts" already
internally, whereas UFS would use gstripe and gmirror as
"little helpers" - it will run on top of them, i. e., you
initialize the device that represents the whole mirror
instead of individually dealing with the drives that the
mirror is constructed of.

Regarding UFS's 2 TB limitation:

Additionally, MBR can be troublesome on bigger hard disks
or stripes.

Today's consensus seems to be:

If you use ZFS, let ZFS deal with everything.

If you use UFS, use gpart for preparation work. Use GPT when
possible, MBR only in exceptions, and dedicated if and only
if you really _really_ know what you're doing. :-)

Magdeburg, Germany
Happy FreeBSD user since 4.0
Andra moi ennepe, Mousa, ...

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