A request for unnested UFS implementation in MBR

Polytropon freebsd at edvax.de
Sat Jul 7 23:47:26 UTC 2018

On Sun, 8 Jul 2018 00:04:37 +0100, RW via freebsd-questions wrote:
> On Sun, 8 Jul 2018 03:28:30 +0530
> Manish Jain wrote:
> > On 07/08/18 03:16, RW via freebsd-questions wrote:
> > > On Sun, 8 Jul 2018 02:20:56 +0530
> > > Manish Jain wrote:
> > >> There is one request I wished to make for FreeBSD filesystems.
> > >> While UFS implementation under GPT is unnested just as Ext2, the
> > >> MBR implementation of UFS continues to piggyback on an unnecessary
> > >> nest (in a BSD slice).
> > > You can put UFS on an MBR partition if you want to.  
> > 
> > How ? Can you give me the gpart command for that ? Remember, the
> > command must put the UFS partition directly into the MBR. Not first
> > into a BSD nest.
> If you create an MBR partition you can run newfs on it - I done this
> for data partitions. Whether or not you can make that a bootable
> partition I don't know, I've never tried. I don't think there's any
> intrinsic reason why it can't be done, it's a matter of whether it's
> supported by a tool.

>From my understanding (and explained off-list), FreeBSD
requires a 'a' BSD-labeled partition (inside a slice in
case of MBR, or on a disk if "dedicated") to boot from.
It doesn't seem to be possible to label a partition 'a'
without using labels.

The label 'c' for data partitions is implicit and will
be synonymous for "the whole thing" (slice, disk), as
it is generated by using newfs on a MBR slice directly
(no matter if "DOS primary partition" or "logical volume
inside DOS extended partition").

> If you just want to put a single  FreeBSD install on a disk without the
> slice you can use a "dangerously dedicated" install, the traditional
> unix install.

Dedicated seems to be out of scope here because a further
intend it to use the FreeBSD boot manager in a multiboot
environment. Reality has shown several times that MBR is
a useful solution here if you want to use that boot manager
exclusively. Linux and FreeBSD can coexist on GPT, too,
but usually require grub for boot selection.

GPT is much more convenient, but it has its limitations.
MBR has limitations as well. And the dedicated approach
should only be used if you exactly know what to expect.

There is no "one size fits all" solution for partitioning,
booting, and multi-booting.

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

More information about the freebsd-questions mailing list