Re: disks, partitions, slices, etc.

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

Oct 2, 2026, 23:50 by martin%duskware.de@localhost:

> On Sat, Oct 03, 2026 at 04:42:46AM +0200, Jeff wrote:
>
>> 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.
>>
>
> I understand the MBR vs. disklabel vs. GPT confusion - it is a disaster
> for historical raisins.
>
> The GPT start is most straigth forward and portable to other OSes:
>
> If you have a disk with GPT it will autoconfigure wedges. So if your
> device is, say, sd0 you can list all wedges with:
>
>  dkctl sd0 listwedges
>
> If your partitions have usefull GPT labels, this should be enough to
> identify them. Example form one machine here:
>
> # dkctl wd0 listwedges
> /dev/rwd0: 2 wedges:
> dk0: G5root, 943718400 blocks at 64, type: ffs
> dk1: G5swap, 56496704 blocks at 943718464, type: swap
>
> my root file system is labeled "G5root", so I can acces it as dk0.
>
> Without label you need to rely on "type", which might not be unique.
> Worst case you get a UUID, and then you may compare it to
>
Ah, thank you! This gives me:

# dkctl ld0 listwedges
/dev/rld0: 7 wedges:
dk0: d4366365-dfba-42c6-aa86-8bd13f5d0564, 2097152 blocks at 2048, type: msdos
dk1: 05a01071-6bc1-481f-b659-a0373ab6d6c8, 33554432 blocks at 2099200, type: 
dk2: 8cf0d625-ed6e-4d4c-9b61-90831ca84c85, 734003200 blocks at 35653632, type: 
dk3: b5bff367-4977-4887-bea0-7e42f7a04fe4, 104857600 blocks at 769656832, type: ext2fs
dk4: c5c7b576-62b3-4a28-b174-8368cd4e15ec, 419430400 blocks at 874514432, type: ext2fs
dk5: f2a6aa99-c65c-4391-925a-97e1ff80a60c, 33550336 blocks at 1293946880, type: swap
dk6: 985d1633-acd7-41c3-b91e-393708c41710, 672909967 blocks at 1327499264, type: ffs

I can tell just from this that dk3 is what I want to work with.
>
>  gpt show -a sd0
>
> output (again assuming your disk is sd0).
>
   769656832   104857600      4  GPT part - Linux data
                                 Type: linux-data
                                 TypeID: 0fc63daf-8483-4772-8e79-3d69d8477de4
                                 GUID: b5bff367-4977-4887-bea0-7e42f7a04fe4
                                 Size: 51200 M
                                 Label: 
                                 Attributes: None

Huh. But in this output, the index of the device I want is 4. So I need to remember not to use the index from this gpt command (which I quite like the output of), but rather the device name from the dkctl command.

By the way, I remember that NetBSD called my SSD 'ld0' in the installer. If I didn't remember that, or if I was working with a system that I didn't install, how would I determine the name of the hard drive?
>
> Once you know the N for your target dkN device, you can create an ext2fs
> file system on it using newfs_ext2fs(8) like:
>
>  newfs_ext2fs -v "myVolume" /dev/rdk0
>
> (if your dkN from the search above is dk0)
>
Okay, so I would be working with /dev/rdk3 then?  Where does that 'r' come from?

Thanks much!
Jeff