Re: disks, partitions, slices, etc.

[Jeff <pacavegano%tutamail.com@localhost>]

Great information, Michael. Thank you!

Jeff
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Oct 2, 2026, 23:51 by mlelstv%serpens.de@localhost:

> pacavegano%tutamail.com@localhost (Jeff) writes:
>
> >I've been reading the documentation and doing searches, and the impression =
> >that I get is that one needs to use entirely different tools to work with M=
> >BR vs GPT partitions, and that most of the documentation is specific to MBR=
> >. Is this true?
>
>
> The distinction is not about MBR vs GPT.
>
>
> NetBSD uses two partitioning schemes:
>
> 1. BSD disklabel (e.g. wd0a, wd0b, wd0c, ...)
> 2. Wedges (e.g. dk0, dk1, dk2, ...)
>
> The BSD disklabel is limited to 32bit block numbers, for regular disks
> (with 512 byte sectors) that limits disk size to 2TB. The disklabel
> is usually stored on the disk but some architectures may use a virtual
> disklabel that is generated from other information.
>
> With wedges, every partition gets its own unit number, there is nothing
> like e.g. "dk0a". Wedges are usually generated from other information,
> the generic kernel supports GPT and Apple (MacOS) partition tables,
> but there are other options too.
>
>
> By default MBR isn't used anywhere, but with MBR you would use BSD disklabel
> and with GPT you would use wedges auto-generated from the GPT.
>
> MBR vs. GPT is more relevant for booting as e.g. a PC BIOS or UEFI firmware
> support either.
>
>
>
> >Based on advice I got elsewhere, I would like to put an ext2 filesystem on =
> >an existing partition that I can share between NetBSD and Gentoo on a dual =
> >boot system. The advice was to create the filesystem from in NetBSD.
>
> That's because NetBSD supports only part of the ext2/ext3/ext4 filesystems
> and creating the filesytem on NetBSD is the easiest way to have something
> understood by both systems.
>
>
>
> >- How do I learn what NetBSD calls the partition that I want to work with.=
> >=C2=A0 For instance, if "fdisk -l" in Linux tells me that it's /dev/sda4, w=
> >hat command can I run in NetBSD to find out what NetBSD calls it?
>
> It may not even be visible.
>
> A 'sda' device on Linux probably corresponds to a 'wd0' device on NetBSD,
> 'sdb' would be 'wd1', etc..  but that depends on the exact hardware.
>
>
> If you are using MBR partitioning, then:
>
> Linux uses MBR partitions directly, so you use /dev/sda1, /dev/sda2, etc
> for the partitions.
>
> On NetBSD you use the BSD disklabel, you have to add an entry for the
> MBR partition to the disklabel with the right offset, size and type. This
> can be done manually with the disklabel program, or you use the mbrlabel
> program to assist. The disklabel partitioned are named 'a' to 'p' (with
> 'a' to 'd' having special meanings). The name is then e.g. /dev/wd0e if
> you use the slot for partition 'e' in the disklabel. But that partition
> letter is something you assign in the disk label, it is independent of
> the partition number used by Linux.
>
>
> If you are using GPT partitioning, then:
>
> Linux uses GPT partitions directly and something like /dev/sda3 would
> be the third partition on the first disk.
>
> NetBSD uses wedge units 'dk0', 'dk1', etc but there is no 1:1 relationship
> and it's even possible (but unlikely for internal disks) that the unit numbers
> change from boot to boot. You can use e.g. 'dkctl wd0 listwedges' to show
> all wedge units that are located on disk 'wd0' (i.e. the first SATA disk).
>
> Since wedge units can change from boot to boot, most tools dealing with
> disks have another way to access them. Each wedge has a unique name,
> that is taken from e.g. the GPT and the tools interpret the syntax
> NAME=<partitonname> and translate it into the right /dev/dk123 unit
> for you.
>
> E.g.:
>
> % dkctl wd1 listwedges
> /dev/rwd1: 6 wedges:
> dk1: gossam-efi, 206814 blocks at 34, type: msdos
> dk2: gossam-root, 819200 blocks at 206848, type: ffs
> dk3: gossam-swap, 134217728 blocks at 1026048, type: swap
> dk4: gossam-usr, 67108864 blocks at 135243776, type: ffs
> dk5: gossam-var, 16777216 blocks at 202352640, type: ffs
> dk6: gossam-home, 3687899136 blocks at 219129856, type: ffs
>
> and an entry in /etc/fstab would look like:
>
> NAME=gossam-usr    /usr      ffs     rw,log                     1    2
>
> N.B. If the GPT doesn't contain such names, there is always a UUID that is
> used as a default name.
>
>
>
> >- Once I know what identifier I should use in NetBSD to refer to the partit=
> >ion (or slice? wedge?), what tool(s) do I use to create the ext2 filesystem=
>
>> on it?
>>
>
> The tool is named newfs_ext2fs.
>
>
> >- Are there any other steps or tools needed that would not occur to me, com=
> >ing from Linux?
>
> The only missing part might the 'gpt' tool that lets you create or edit the GPT
> stored on a disk.
>