Re: How to replace a missing device with a smaller one

[Nathan Dehnel <ncdehnel@gmail.com>]

The patch worked. Thanks for the help.

On Mon, Nov 18, 2019 at 1:08 AM Qu Wenruo <quwenruo.btrfs@gmx.com> wrote:
>
>
>
> On 2019/11/18 下午1:32, Qu Wenruo wrote:
> >
> >
> > On 2019/11/18 上午10:09, Nathan Dehnel wrote:
> >> I have a 10-disk raid10 with a missing device I'm trying to replace. I
> >> get this error when doing it though:
> >>
> >> btrfs replace start 1 /dev/bcache0 /mnt
> >> ERROR: target device smaller than source device (required 1000203091968 bytes)
> >>
> >> I see that people recommend resizing a disk before replacing it, which
> >> isn't an option for me because it's gone.
> >
> > Oh, that's indeed a problem.
> >
> > We should allow to change missing device's size.
>
> I have CCed you with a patch to allow user to *shrink* the missing device.
>
> You can also get the patch from patchwork:
> https://patchwork.kernel.org/patch/11249009/
>
> Please give a try, since the device size is pretty small, I believe with
> that patch, we can go quick shrink, that means "btrfs fi resize" command
> should return immediately.
>
> Then you can go regular replace, this should save you a lot of IO by
> avoiding the IO/time consuming device removal.
>
> Thanks,
> Qu
>
> >
> >> I'm replacing the drive by
> >> copying from its mirror, so can I resize the mirror and then replace?
> >> How do I do that? Do I need to run "btrfs fi res" on each of the
> >> remaining drives in the array?
> >>
> > As a workaround, you could remove that missing device (which would
> > relocate all chunks using it, so it can be slow).
> >
> > Then add the new device to the fs.
> >
> > With that done, it's recommended to do a convert to take full use the
> > two added devices.
> >
> > Thanks,
> > Qu
> >
>