Only one subvolume can be mounted after replace/balance

Only one subvolume can be mounted after replace/balance

[Jakob Schöttl]

Hi,

In short:
When mounting a second subvolume from a pool, I get this error:
"mount: /mnt: wrong fs type, bad option, bad superblock on /dev/sda, 
missing code page or helper program, or other."
dmesg | grep BTRFS only shows this error:
info (device sda): disk space caching is enabled
error (device sda): Remounting read-write after error is not allowed

What happened:

In my RAID1 pool with two disk, I successfully replaced one disk with

btrfs replace start 2 /dev/sdx

After that, I mounted the pool and did

btrfs fi show /mnt

which showed WARNINGs about
"filesystems with multiple block group profiles detected"
(don't remember exactly)

I thought it is a good idea to do

btrfs balance start /mnt

which finished without errors.

Now, I can only mount one (sub)volume of the pool at a time. Others can 
only be mounted read-only. See error messages at top of this mail.

Do you have any idea what happened or how to fix it?

I already tried rescue zero-log and super-recovery which was successful 
but didn't help.

Regards, Jakob

Re: Only one subvolume can be mounted after replace/balance

[Chris Murphy]

On Sat, Jan 23, 2021 at 7:50 AM Jakob Schöttl <jschoett@gmail.com> wrote:
>
> Hi,
>
> In short:
> When mounting a second subvolume from a pool, I get this error:
> "mount: /mnt: wrong fs type, bad option, bad superblock on /dev/sda,
> missing code page or helper program, or other."
> dmesg | grep BTRFS only shows this error:
> info (device sda): disk space caching is enabled
> error (device sda): Remounting read-write after error is not allowed

It went read-only before this because it's confused. You need to
unmount it before it can be mounted rw. In some cases a reboot is
needed.

>
> What happened:
>
> In my RAID1 pool with two disk, I successfully replaced one disk with
>
> btrfs replace start 2 /dev/sdx
>
> After that, I mounted the pool and did

I don't understand this sequence. In order to do a replace, the file
system is already mounted.

>
> btrfs fi show /mnt
>
> which showed WARNINGs about
> "filesystems with multiple block group profiles detected"
> (don't remember exactly)
>
> I thought it is a good idea to do
>
> btrfs balance start /mnt
>
> which finished without errors.

Balance alone does not convert block groups to a new profile. You have
to explicitly select a conversion filter, e.g.

btrfs balance start -dconvert=raid1,soft -mconvert=raid1,soft /mnt

> Now, I can only mount one (sub)volume of the pool at a time. Others can
> only be mounted read-only. See error messages at top of this mail.
>
> Do you have any idea what happened or how to fix it?
>
> I already tried rescue zero-log and super-recovery which was successful
> but didn't help.

I advise anticipating the confusion will get worse, and take the
opportunity to refresh the backups. That's the top priority, not
fixing the file system.

Next let us know the following:

kernel version
btrfs-progs version
Output from commands:
btrfs fi us /mnt
btrfs check --readonly


-- 
Chris Murphy

Re: Only one subvolume can be mounted after replace/balance

[Jakob Schöttl]

Thank you Chris, it's resolved now, see below.

Am 25.01.21 um 23:47 schrieb Chris Murphy:
> On Sat, Jan 23, 2021 at 7:50 AM Jakob Schöttl <jschoett@gmail.com> wrote:
>> Hi,
>>
>> In short:
>> When mounting a second subvolume from a pool, I get this error:
>> "mount: /mnt: wrong fs type, bad option, bad superblock on /dev/sda,
>> missing code page or helper program, or other."
>> dmesg | grep BTRFS only shows this error:
>> info (device sda): disk space caching is enabled
>> error (device sda): Remounting read-write after error is not allowed
> It went read-only before this because it's confused. You need to
> unmount it before it can be mounted rw. In some cases a reboot is
> needed.
Oh, I didn't notice that the pool was already mounted (via fstab).
The filesystem where out of space and I had to resize both disks 
separately. And I had to mount with -o skip_balance for that. Now it 
works again.

>> What happened:
>>
>> In my RAID1 pool with two disk, I successfully replaced one disk with
>>
>> btrfs replace start 2 /dev/sdx
>>
>> After that, I mounted the pool and did
> I don't understand this sequence. In order to do a replace, the file
> system is already mounted.
That was, what I did before my actual problem occurred. But it's 
resolved now.

>> btrfs fi show /mnt
>>
>> which showed WARNINGs about
>> "filesystems with multiple block group profiles detected"
>> (don't remember exactly)
>>
>> I thought it is a good idea to do
>>
>> btrfs balance start /mnt
>>
>> which finished without errors.
> Balance alone does not convert block groups to a new profile. You have
> to explicitly select a conversion filter, e.g.
>
> btrfs balance start -dconvert=raid1,soft -mconvert=raid1,soft /mnt
I didn't want to convert to a new profile. I thought btrfs replace 
automatically uses the same profile as the pool?

Regards, Jakob

Re: Only one subvolume can be mounted after replace/balance

[Chris Murphy]

On Wed, Jan 27, 2021 at 6:10 AM Jakob Schöttl <jschoett@gmail.com> wrote:
>
> Thank you Chris, it's resolved now, see below.
>
> Am 25.01.21 um 23:47 schrieb Chris Murphy:
> > On Sat, Jan 23, 2021 at 7:50 AM Jakob Schöttl <jschoett@gmail.com> wrote:
> >> Hi,
> >>
> >> In short:
> >> When mounting a second subvolume from a pool, I get this error:
> >> "mount: /mnt: wrong fs type, bad option, bad superblock on /dev/sda,
> >> missing code page or helper program, or other."
> >> dmesg | grep BTRFS only shows this error:
> >> info (device sda): disk space caching is enabled
> >> error (device sda): Remounting read-write after error is not allowed
> > It went read-only before this because it's confused. You need to
> > unmount it before it can be mounted rw. In some cases a reboot is
> > needed.
> Oh, I didn't notice that the pool was already mounted (via fstab).
> The filesystem where out of space and I had to resize both disks
> separately. And I had to mount with -o skip_balance for that. Now it
> works again.
>
> >> What happened:
> >>
> >> In my RAID1 pool with two disk, I successfully replaced one disk with
> >>
> >> btrfs replace start 2 /dev/sdx
> >>
> >> After that, I mounted the pool and did
> > I don't understand this sequence. In order to do a replace, the file
> > system is already mounted.
> That was, what I did before my actual problem occurred. But it's
> resolved now.
>
> >> btrfs fi show /mnt
> >>
> >> which showed WARNINGs about
> >> "filesystems with multiple block group profiles detected"
> >> (don't remember exactly)
> >>
> >> I thought it is a good idea to do
> >>
> >> btrfs balance start /mnt
> >>
> >> which finished without errors.
> > Balance alone does not convert block groups to a new profile. You have
> > to explicitly select a conversion filter, e.g.
> >
> > btrfs balance start -dconvert=raid1,soft -mconvert=raid1,soft /mnt
> I didn't want to convert to a new profile. I thought btrfs replace
> automatically uses the same profile as the pool?

Btrfs replace does not change the profile. But you reported mixed
profile block groups, which means conversion is indicated to make sure
they're al the same. Please post:

sudo btrfs fi us /mnt

Let's see what the block groups are and what you want them to be and
then see what conversion command might be indicated.


-- 
Chris Murphy