On 16/09/18, Chris Murphy (lists@xxxxxxxxxxxxxxxxx) wrote:
> > So I did this:
> >
> > btrfs subvol snapshot /bkp /bkp/backup-subvol
> >
> > strangely while /bkp/backup has lots of files in it,
> > /bkp/backup-subvol/backup has none.
> >
> > # btrfs subvol list /bkp
> > ID 258 gen 313585 top level 5 path backup
> > ID 4782 gen 313590 top level 5 path backup-subvol
>
> OK so previously you said "/bkp which is a top level subvolume. There
> are no other subvolumes."
>
> But in fact backup is already a subvolume. So now it's confusing what
> you were asking for in the first place, maybe you didn't realize
> backup is not a dir but it is a subvolume.
Thanks very much for spotting my error, Chris.
# mount | grep bkp
/dev/mapper/cdisk2 on /bkp type btrfs
(rw,noatime,compress=lzo,space_cache,subvolid=5,subvol=/)
# btrfs subvol list /bkp
ID 258 gen 313636 top level 5 path backup
I'm a bit confused about the difference between / and backup, which is
at /bkp/backup.
Anyhow I've verified I can snapshot /bkp/backup to another subvolume.
This means I don't need to move anything, simply remount /bkp at
/bkp/backup.
Presumably I can therefore remount /bkp at subvolume /backup?
# btrfs subvolume show /bkp/backup | egrep -i 'name|uuid|subvol'
Name: backup
UUID: d17cf2ca-a6db-ca43-8054-1fd76533e84b
Parent UUID: -
Received UUID: -
Subvolume ID: 258
My fstab is presently
UUID=da90602a-b98e-4f0b-959a-ce431ac0cdfa /bkp btrfs noauto,noatime,compress=lzo 0 2
I guess it would now be
UUID=d17cf2ca-a6db-ca43-8054-1fd76533e84b /bkp btrfs noauto,noatime,compress=lzo 0 2
> If you snapshot a subvolume, which itself contains subvolumes, the
> nested subvolumes are not snapshot. In the snapshot, the nested
> subvolumes are empty directories.
>
> >
> > # btrfs fi du -s /bkp/backup-subvol/backup
> > Total Exclusive Set shared Filename
> > ERROR: cannot check space of '/bkp/backup-subvol/backup': Inappropriate
> > ioctl for device
>
> That's a bug in older btrfs-progs. It's been fixed, but I'm not sure
> what version, maybe by 4.14?
Sounds about right -- my version is 4.7.3.
> > Any ideas about what could be going on?
> >
> > In the mean time I'm trying:
> >
> > btrfs subvol create /bkp/backup-subvol
> > cp -prv --reflink=always /bkp/backup/* /bkp/backup-subvol/
>
> Yeah that will take a lot of writes that are not necessary, now that
> you see backup is a subvolume already. If you want a copy of it, just
> snapshot it.
Makes sense.
Thanks very much
Rory
