Re: disks, partitions, slices, etc.

[Jeff <pacavegano%odonian.org@localhost>]

Just to follow up with results:

I did create the ext2 filesystem with "newfs_ext2fs", then I mounted it 
in NetBSD and created some test files.  I rebooted into Gentoo and tried 
to mount it, but got an error about a block overlap, saying that the 
filesystem needed to be repaired.

I logged back into NetBSD and ran fsck_ext2fs on it, which did not 
report anything. Then rebooted into Gentoo and still got the error. So I 
ran fsck on it in Gentoo. It moved a ton of blocks, periodically warning 
of the potential for data loss. When it was done, I was able to mount 
the partition in Gentoo. The text file that I had created in the top 
level of the partition in NetBSD was still there, but the directory 
containing two other test files was gone. I recreated them in Gentoo, 
then rebooted into NetBSD. The partition still mounted fine there, and 
all files that had been visible in Gentoo were present.

So, what worked for me was:
- create ext2 filesystem in NetBSD
- fsck it in NetBSD (possibly unnecessary)
- fsck it in Gentoo

I'll continue to test it going back and forth and see if it's stable now.

Thanks again,
Jeff

On 10/3/26 09:27, Jeff wrote:
> 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