ubuntu bionic grub can't boot zstd compressed filesystem

[en]

In the /etc/fstab of installed ubuntu bionic system I specified compress=zstd for the btrfs root filesytem
After runing 'sudo btrfs filesystem defragment -r -czstd /' the system booted to a grub shell. I could boot again by running 'sudo btrfs filesystem defragment -r -clzo /' and specifying compress=lzo in the /etc/fstab.
There is also a new bug in the btrfs tools:
btrfs does recognize the option '-clzo' but not '-c lzo'.

[Dimitri John Ledkov (xnox)]

I wonder if I should be disabling zstd support in btrfs-progs, if we cannot boot them.

[Lorens Gwine (lorensgwine)]

There may be non root partitions that users want to compress with zstd so you shouldn't

[en (b21enu)]

possible workaround:
Patch all btrfs-tools so that they don't compress files accessed by grub with zstd.

pitfall:
If users repair the filesystem from a live-cd, (eg. run defragmentation), they must make sure that they don't compress files acessed by grub with zstd.

Another option:
Archlinux uses this patched grub version:

https://github.com/Antynea/grub-btrfs

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.

[Konstantin (hi-angel-z)]

> Another option:
> Archlinux uses this patched grub version:
>
> https://github.com/Antynea/grub-btrfs

This is doubly wrong. Archlinux does not use what you linked, but instead uses mainline version with some patches https://git.archlinux.org/svntogit/packages.git/tree/trunk/PKGBUILD?h=packages/grub#n60 Either way, it doesn't work for the topic.

But I (I'm on Archlinux) did try your github version, there's a user package grub-btrfsᴬᵁᴿ for this one. It does not boot from zstd compressed partition either.

[Mathieu Trudel-Lapierre (cyphermox)]

This would be an enhancement request.

[Dmitriy Geels (dmig)]

The simplest workaround for the moment:

sudo btrfs property set /boot compression lzo # ensure this dir will remain readable by grub
sudo btrfs filesystem defragment -vr /boot # ensure /boot gets recompressed

[Dmitriy Geels (dmig)]

Seems that btrfs ignores compression attribute if compression was set using mount option.
So, the solution is to set compression attributes per-directory:

1) remove 'compress=zstd' from your fstab root record
2) sudo btrfs property set /boot compression lzo # ensure this dir will remain readable by grub
3) sudo btrfs filesystem defragment -vrclzo /boot # ensure /boot gets recompressed
4) for $d in bin etc lib lib64 opt sbin snap srv usr var; do sudo btrfs property set /$d compression zstd; done

Directory list is for Ubuntu 18, check and adjust for your own needs.

[Dmitriy Geels (dmig)]

Results (using btrfs-compsize tool):

$ sudo compsize /boot/ /bin/ /usr/
Processed 240794 files, 88025 regular extents (89183 refs), 162022 inline.
Type Perc Disk Usage Uncompressed Referenced
TOTAL 50% 2.7G 5.3G 5.4G
none 100% 1.1G 1.1G 1.1G
lzo 46% 9.1M 19M 19M
zstd 37% 1.5G 4.1G 4.2G