Arch Linux

shoelesshunter

Member

From: USA

Registered: 2014-05-18

Posts: 289

[solved] btrfs read-only after an attempted balance -mconvert=dup

I have a single disk btrfs root on a luks volume. separate /boot.
data was single. metadata was single. I was advised to change meta to DUP and did

 btrfs balance start -mconvert DUP /mnt

I had 150GB free of a total of 2TB, yet the fs went r/o immediately.
a reboot asked for my luks passphrase, then dropped me into a recovery. where I was instructd to press 'ctr d' for maintenance,  but no input was accepted. I use grub-btrfs, and I was able to reboot again, this time selecting an older r/o snapshot. the volume was unlocked, and I booted into a busybox environment with no btrfs-progs
I was able to mount the top level subvolume with

mkdir /ssd && mount -o rw,skip_balance /dev/mapper/cryptssd /ssd

everything looks intact
however

touch /ssd/test

gives an I/O error. in my current situation, I have no live media to boot from nor secondary storage.

Last edited by shoelesshunter (2022-06-19 14:07:39)

tsweet64

Member

Registered: 2021-04-29

Posts: 14

Re: [solved] btrfs read-only after an attempted balance -mconvert=dup

Run `journalctl -eb` immediately after mounting and examine any btrfs-related output in the log. This should indicate which error the kernel is encountering when attempting to mount and can help troubleshoot further.

shoelesshunter

Member

From: USA

Registered: 2014-05-18

Posts: 289

Re: [solved] btrfs read-only after an attempted balance -mconvert=dup

when I boot the default kernel, I get the prompt to run journalctl but the system doesn't accept any input. when I boot into a non-existent snapshot, (grub has the entry, but they've been deleted), I find myself in busy box environment. here I am able to mount the fs, but it still mounts r/o even with

 -o skip_balance,rw

Last edited by shoelesshunter (2022-06-19 14:10:00)

tsweet64

Member

Registered: 2021-04-29

Posts: 14

Re: [solved] btrfs read-only after an attempted balance -mconvert=dup

Try `dmesg` instead to get the log. Depending on what it says, you'll probably need to find some way to get btrfs-progs if you didn't include it in your initramfs. I'm not sure how without an archiso, perhaps someone else knows

shoelesshunter

Member

From: USA

Registered: 2014-05-18

Posts: 289

Re: [solved] btrfs read-only after an attempted balance -mconvert=dup

I solved this by booting kernel 4.19. I was then able to

mount -o skip_balance,rw /dev/mapper/cryptssd /mnt

then

btrfs balance cancel /mnt

I ran a filtered balance:

btrfs balance start -musage=5 -dusage=10 /mnt

after freeing up some space I finally ran

btrfs balance start -mconvert=dup /mnt

all of this was done on kernel 4.19

I rebooted the fs and it is r/w.

the problem is that I was never truly out of free space. there is a know bug in 5.x where a balance with -mconvert=dup will do two critical things. first, the fs thinks it is out of free space and locks r/o. second,

mount -o rw,skip_balance

is ignored, and every time one attempts to remount the drive, the balance tries to resume and the fs immediately locks r/o.

https://www.reddit.com/r/btrfs/comments … cancel_no/

note: I'm not sure

btrfs balance start -musage=5 -dusage=10 /mnt

was necessary, but it was recommended.