Re: zfs and device name changes

[Takashi YAMAMOTO <yamt9999%gmail.com@localhost>]

hi,

On Thu, Mar 26, 2026 at 12:41 PM Taylor R Campbell <riastradh%netbsd.org@localhost> wrote:
>
> > Date: Tue, 24 Mar 2026 09:14:37 +0900
> > From: Takashi YAMAMOTO <yamt9999%gmail.com@localhost>
> >
> > the attached patch is my attempt to make zfs a bit more robust against
> > device name changes.
> > the identical patch is available at github too:
> > https://github.com/yamt/netbsd-src/commit/32283c2e362034301c3da218a05849c04ee20c2a
> >
> > while it seems working as far as i tested, i'd be happy if someone can review it
> > as my knowledge of zfs (well, and recent netbsd in general) is weak.
>
> I don't understand why all this new code is needed.  Doesn't zfs
> already have logic to scan all disks/partitions/wedges and find the
> vdevs by guid?

which code are you talking about?
it's entirely possible i'm missing something as i'm new to the code base.

>
> I am under the impression that /etc/zfs/zpool.cache may bypass the
> scan so this doesn't work in some circumstances, but in my years of
> using zfs on various machines with frequent device renumbering of cgd
> volumes and dkN wedges, I have never encountered this type of trouble
> myself, and I'm not sure what I'm doing differently.

do you mean zfs finds vdevs after renumbering without zpool import?
it doesn't match my experience.
without this patch, i had to use zpool export/import after:
- modify gpt in a way affecting dk numbering
- swapping qemu disk images