Re: [PATCH] btrfs-progs: default to SINGLE profile on zoned devices

[David Sterba <dsterba@suse.cz>]

On Mon, Jul 12, 2021 at 07:16:36PM +0000, Johannes Thumshirn wrote:
> On 07/07/2021 17:02, Johannes Thumshirn wrote:
> > On 07/07/2021 16:53, David Sterba wrote:
> >> On Tue, Jul 06, 2021 at 06:19:22PM +0900, Johannes Thumshirn wrote:
> >>> On zoned devices we're currently not supporting any other block group
> >>> profile than the SINGLE profile, so pick it as default value otherwise a
> >>> user would have to specify it manually at mkfs time for rotational zoned
> >>> devices.
> >>
> >> Yes this is annoying but careful with setting defaults, it's hard to
> >> change them. And in case of zoned devices it will be possible to set
> >> something else in the future so defaulting to single/single needs to be
> >> justified in another way than "currently we don't support anything
> >> else".
> >>
> >> The SSD fallback to single is not showing as useful and there's ongoing
> >> work to make it default to dup for metadata again. For consistency I'd
> >> rather have simple logic for selecting defaults and give hints
> >> eventually instead of checking random things in the system and then
> >> selectin on behalf of the user. Unfortunatelly it's not that easy as
> >> there are conflicting valid interests and we don't have defaults that
> >> fits all scenarios.
> >>
> > 
> > Agreed, but without this patch mkfs with default parameters on a rotational
> > zoned device will fail with:
> > 
> > johannes@redsun60:btrfs-progs(master)$ sudo ./mkfs.btrfs /dev/sda
> > btrfs-progs v5.12.1 
> > See http://btrfs.wiki.kernel.org for more information.
> > 
> > Zoned: /dev/sda: host-managed device detected, setting zoned feature
> > ERROR: cannot use RAID/DUP profile in zoned mode
> > 
> > So defaulting to not creating a filesystem won't work either.
> > 
> > We could improve the error message hinting the user to specify 
> > "-m single -d single" on mkfs but that feels more hacky than setting 
> > the defaults to something working.
> > 
> 
> So what's the way to go here? The current default won't create a file
> system so it's unusable.

I've updated the message to ask for -d single -m single.