Re: Btrfs subvolume question

[Robert White <rwhite@pobox.com>]

On 02/04/2015 06:27 PM, Chris Murphy wrote:
> On Wed, Feb 4, 2015 at 3:54 PM, Markus Moeller <huaraz@moeller.plus.com> wrote:
>> Hi ,
>>
>>    I am new to btrfs and wonder what I need to do to move subvolumes to the
>> right filesystem.  I see the following:
>>
>> df -h
>> Filesystem                       Size  Used Avail Use% Mounted on
>> /dev/mapper/system_13.2-root_lv  5.0G  1.5G  3.2G  32% /
>> devtmpfs                         235M  8.0K  235M   1% /dev
>> tmpfs                            242M   84K  242M   1% /dev/shm
>> tmpfs                            242M  2.4M  240M   1% /run
>> tmpfs                            242M     0  242M   0% /sys/fs/cgroup
>> /dev/mapper/system_13.2-usr_lv    18G  6.9G   10G  41% /usr
>> /dev/mapper/system_13.2-root_lv  5.0G  1.5G  3.2G  32% /srv
>> /dev/mapper/system_13.2-root_lv  5.0G  1.5G  3.2G  32% /.snapshots
>> /dev/mapper/system_13.2-root_lv  5.0G  1.5G  3.2G  32% /tmp
>> /dev/mapper/system_13.2-root_lv  5.0G  1.5G  3.2G  32% /usr/local
>> /dev/sda2                        486M   59M  398M  13% /boot
>> /dev/mapper/system_13.2-root_lv  5.0G  1.5G  3.2G  32%
>> /boot/grub2/x86_64-efi
>> /dev/mapper/system_13.2-root_lv  5.0G  1.5G  3.2G  32% /boot/grub2/i386-pc
>> /dev/mapper/export_vg-export_lv   20G   18G  2.9G  86% /export
>> /dev/mapper/export_vg-src_lv     5.0G  2.6G  2.5G  51% /src
>> /dev/mapper/system_13.2-var_lv   4.0G  196M  3.4G   6% /var
>> /dev/mapper/system_13.2-opt_lv   6.0G  152M  5.3G   3% /opt
>> /dev/mapper/system_13.2-root_lv  5.0G  1.5G  3.2G  32% /var/spool
>> /dev/mapper/system_13.2-root_lv  5.0G  1.5G  3.2G  32% /var/tmp
>> /dev/mapper/system_13.2-root_lv  5.0G  1.5G  3.2G  32% /var/opt
>> /dev/mapper/system_13.2-root_lv  5.0G  1.5G  3.2G  32% /var/log
>> /dev/mapper/system_13.2-root_lv  5.0G  1.5G  3.2G  32% /var/lib/named
>> /dev/mapper/system_13.2-root_lv  5.0G  1.5G  3.2G  32% /var/lib/mailman
>> /dev/mapper/system_13.2-root_lv  5.0G  1.5G  3.2G  32% /var/lib/pgsql
>>
>>
>> and I would like to have all the var subvolumes using the /var filesystem
>> space and not root.  The same for /boot/grub2 subvolumes. They should use
>> the /boot filesystem.
>
> The giveaway is in the first column. All of these are device mapper
> LVM LV's, they are not Btrfs subvolumes, in fact they're separate
> Btrfs volumes (unique, unrelated filesystems). What's suspicious,
> though, is that a bunch of these LV's have exactly 1.5G Used, which
> makes no sense. For example, /boot/grub2/i386-pc has 1.5G used, but
> that's not possible, the entire GRUB2 package is maybe 50MB.

Actually given that the first column repeats 
/dev/mapper/system_13.2-root_lv as the device, I think he's repeatedly 
mounted the same device filesystem with different subovol= directives.

That's why so many of them have the same 1.5G used.

In terms of actual LVs he only seems to have _root_ _opt_ _var_ and 
_usr_ once you strip away the various noise components.

In particular oddity fassion /var is a different device but /var/log 
goes back to the root device.

In a slightly over-thought way its kind of twisted genius if you view 
/var/lib/named and such as being tightly bound to /etc. (/var/tmp is 
totally wrong.)

It's not something I would want to maintain either.

They also might be bind mounts instead of subvol= mounts. I'd have to 
see /etc/fstab.

The output of btrfs subvol list  on / /var /usr and /opt would be nice 
as well.


>
> Honestly, I suggest reinstalling and don't deal with the tricky task
> of converting all of this. It'll take longer for me to explain, and
> you to read, how to fix this without reinstalling. I also suggest
> making sure that you don't put Btrfs on LVM, there's no good reason to
> do this for most use cases.
>
>
>   I don't know how I got to this and don't know how to
>> change.
>
> It's not your fault. This is a pathological side effect of openSUSE
> 13.2's, quite frankly bizarre, layout. By default it creates a single
> Btrfs volume, and makes all of these subvolumes, which is strange
> enough on its own because it's overly complicated (just look at
> /etc/fstab) for no good reason. But somehow in your case, you ended up
> with a bunch of LVM LVs first, and then each of those is a Btrfs
> volume. If it were me, I'd file a bug report against 13.2, and then
> file a feature request citing the bug report. If you don't want to do
> both, then just file the feature request against Factory because
> installer related bug reports on openSUSE basically get rejected
> seeing as there's nothing that can be done about it in Distribution
> now anyway.
>