Re: Questions related to BCacheFS

[Martin Steigerwald <martin@lichtvoll.de>]

Kent Overstreet - 20.11.23, 00:10:01 CET:
> Maybe I need to continue testing BCacheFS on a virtual machine, but I'd
> 
> > really love to have a BCacheFS filesystem on my laptop and actually
> > really using it for something. Well I am going to leave it at that
> > and probably research on this after the weekend. Now it is time to
> > have a Sunday off.
> The Nixos install process with bcachefs as root is pretty smooth, just
> make sure to set up a separate filesystem for /boot!

Thanks for that idea.

While it might have been that those BTRFS filesystems that got corrupted 
where corrupted by an "thou shalt not resume from this hibernation image" 
I will indeed wait before I try 5.7 kernel again on this laptop. Also I 
will likely wait for an update bcachefs-tools package. I still don't know 
why GRUB greeted me with a command prompt after having removed 5.7 kernel 
again. My current idea on why the BTRFS corruption happened is cause of 
kernel 6.6.1 resuming from hibernation after I fixed up the boot loader in 
two GRML sessions, accessing / and /boot, but not doing anything to 
invalidate the hibernation image on the swap volume. Reminder to self: 
Absolutely do that next time!

I had to restore / and /home BTRFS filesystem as well as /boot, which got 
GRUB broken once more:

xfsprogs-6.5.0 with grub 2.12~rc1-12: unknown filesystem

https://lore.kernel.org/linux-xfs/1889442.tdWV9SEqCh@lichtvoll.de/T/#t

So yes I am very well aware of the advantages of a separate /boot. But 
even with that GRUB was funny on me. Maybe that is why I have seen Ext4 in 
Ext3 mode for /boot. It does not gain new features.

I may investigate an alternative boot loader… it is not the first time GRUB 
broke on new filesystem features and it is not even surprising. It would be 
best to have GRUB use a very simple file system that does not gain new 
features. A bootfs filesystem just for the purposes of a boot loader to 
store a few files and be done with it.

Anyway, it will be a VM for now.

Ciao,
-- 
Martin