[systemd-devel] No space left errors on shutdown with systemd-homed /home dir

[Neal Gompa]

On Tue, Feb 1, 2022 at 2:02 PM Colin Guthrie <colin at booksterhq.com> wrote:
>
> Goffredo Baroncelli wrote on 30/01/2022 09:27:
> > On 29/01/2022 19.01, Chris Murphy wrote:
> >> On Sat, Jan 29, 2022 at 2:53 AM Goffredo Baroncelli
> >> <kreijack at libero.it> wrote:
> >>>
> >>> I think that for the systemd uses cases (singled device FS), a simpler
> >>> approach would be:
> >>>
> >>>       fstatfs(fd, &sfs)
> >>>       needed = sfs.f_blocks - sfs.f_bavail;
> >>>       needed *= sfs.f_bsize
> >>>
> >>>       needed = roundup_64(needed, 3*(1024*1024*1024))
> >>>
> >>> Comparing the original systemd-homed code, I made the following changes
> >>> - 1) f_bfree is replaced by f_bavail (which seem to be more
> >>> consistent to the disk usage; to me it seems to consider also the
> >>> metadata chunk allocation)
> >>> - 2) the needing value is rounded up of 3GB in order to consider a
> >>> further 1 data chunk and 2 metadata chunk (DUP))
> >>>
> >>> Comments ?
> >>
> >> I'm still wondering if such a significant shrink is even indicated, in
> >> lieu of trim. Isn't it sufficient to just trim on logout, thus
> >> returning unused blocks to the underlying filesystem?
> >
> > I agree with you. In Fedora 35, and the default is ext4+luks+trim
> > which provides the same results. However I remember that in the past the
> > default
> > was btrfs+luks+shrunk. I think that something is changed i.
> >
> > However, I want to provide do the systemd folks a suggestion ho change
> > the code.
> > Even a warning like: "it doesn't work that because this, please drop it"
> > would be sufficient.
>
>
> Out of curiosity (see other thread on the systemd list about this), what
> it the current recommendation (by systemd/btrfs folks rather then Fedora
> defaults) for homed machine partitioning?
>

I'd probably recommend Btrfs with the /home subvolume set with
nodatacow if you're going to use loops of LUKS backed Btrfs homedir
images. The individual Btrfs loops will have their own COW anyway.

Otherwise, the Fedora defaults for Btrfs should be sufficient.



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