Re: [PATCH 0/3] btrfs: More intelligent degraded chunk allocator

David Sterba
2019-11-27T19:26:17Z

On Tue, Nov 19, 2019 at 01:18:21PM +0800, Alberto Bursi wrote:
> >> Thanks. This is going to change the behaviour with a missing device, so
> >> the question is if we should make this configurable first and then
> >> switch the default.
> > Configurable then switch makes sense for most cases, but for this
> > degraded chunk case, IIRC the new behavior is superior in all cases.
> >
> > For 2 devices RAID1 with one missing device (the main concern), old
> > behavior will create SINGLE/DUP chunk, which has no tolerance for extra
> > missing devices.
> >
> > The new behavior will create degraded RAID1, which still lacks tolerance
> > for extra missing devices.
> >
> > The difference is, for degraded chunk, if we have the device back, and
> > do proper scrub, then we're completely back to proper RAID1.
> > No need to do extra balance/convert, only scrub is needed.
> >
> > So the new behavior is kinda of a super set of old behavior, using the
> > new behavior by default should not cause extra concern.
>
> I think most users will see this as a bug fix, as the current behavior
> of creating
>
> SINGLE chunks is very annoying and can cause confusion as it is NOT an
>
> expected behavior for a classic (mdadm or hardware) degraded RAID array.

Thanks for the feedback, I agree with that. It's good to have a
confirmation from somebody outside of developer group.