Re: Which device is missing ?

[Hugo Mills <hugo@carfax.org.uk>]

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On Mon, Oct 08, 2018 at 11:01:35PM +0200, Pierre Couderc wrote:
> On 10/08/2018 06:14 PM, Hugo Mills wrote:
> >On Mon, Oct 08, 2018 at 04:10:55PM +0000, Hugo Mills wrote:
> >>On Mon, Oct 08, 2018 at 03:49:53PM +0200, Pierre Couderc wrote:
> >>>I ma trying to make a "RAID1" with /dev/sda2 ans /dev/sdb (or similar).
> >>>
> >>>But I have stranges status or errors  about "missing devices" and I
> >>>do not understand the current situation :
> >>>
> >>>
> >>>root@server:~# btrfs fi show
> >>>Label: none  uuid: 28c2b7ab-631c-40a3-bab7-00dac5dd20eb
> >>>         Total devices 1 FS bytes used 190.91GiB
> >>>         devid    1 size 1.82TiB used 196.02GiB path /dev/sda2
> >>>
> >>>warning, device 1 is missing
> >>>Label: none  uuid: 2d45149a-fb97-4c2a-bae2-4cfe4e01a8aa
> >>>         Total devices 2 FS bytes used 116.18GiB
> >>>         devid    2 size 1.82TiB used 118.03GiB path /dev/sdb
> >>>         *** Some devices missing
> >>    This looks like you've created a RAID-1 array with /dev/sda2 and
> >>/dev/sdb, and then run mkfs.btrfs again on /dev/sda2, overwriting the
> >>original [part of a] filesystem on /dev/sda2, and replacing it with a
> >>wholly different filesystem. Since the new FS on /dev/sda2 (UUID
> >>28c2...) doesn't have the same UUID as the original FS (UUID 2d45...),
> >>and the original FS was made of two devices, btrfs fi show is telling
> >>you that there's some devices missing -- /dev/sda2 is no longer part
> >>of that FS, and is therefore a missing device.
> >>
> >>    I note that you've got data on both filesystems, so they must both
> >>have been mounted somewhere and had stuff put on them.
> >>
> >>    I recommend doing something like this:
> >>
> >># mkfs /media/btrfs/myraid1 /media/btrfs/tmp
> >># mount /dev/sdb /media/btrfs/myraid1/
> >># mount /dev/sda2 /media/btrfs/tmp/              # mount both filesystems
> >># cp /media/btrfs/tmp/* /media/btrfs/myraid1     # put it where you want it
> >># umount /media/btrfs/tmp/
> >># wipefs /dev/sda2                               # destroy the FS on sda2
> >># btrfs replace start 1 /dev/sda2 /media/btrfs/myraid1/
> >>
> >>    This will copy all the data from the filesystem on /dev/sda2 into
> >>the filesystem on /dev/sdb, destroy the FS on sda2, and then use sda2
> >>as the second device for the main FS.
> >>
> >>*WARNING!*
> >>
> >>    Note that, since the main FS is missing a device, it will probably
> >>need to be mounted in degraded mode (-o degraded), and that on kernels
> >>earlier than (IIRC) 4.14, this can only be done *once* without the FS
> >>becoming more or less permanently read-only. On recent kernels, it
> >>_should_ be OK.
> >>
> >>*WARNING ENDS*
> >    Oh, and for the record, to make a RAID-1 filesystem from scratch,
> >you simply need this:
> >
> ># mkfs.btrfs -m raid1 -d raid1 /dev/sda2 /dev/sdb
> >
> >    You do not need to run mkfs.btrfs on each device separately.
> >
> >    Hugo.
> Thnk you very much. I understand a bit better. I think  that I have
> nothing of interest on /dev/sdb and that its contents is the result
> of previous trials.
> And that my system is on /dev/dsda2 as :
> 
> root@server:~# df -h
> Filesystem      Size  Used Avail Use% Mounted on
> udev            3.9G     0  3.9G   0% /dev
> tmpfs           787M  8.8M  778M   2% /run
> /dev/sda2       1.9T  193G  1.7T  11% /
> tmpfs           3.9G     0  3.9G   0% /dev/shm
> tmpfs           5.0M     0  5.0M   0% /run/lock
> tmpfs           3.9G     0  3.9G   0% /sys/fs/cgroup
> /dev/sda1       511M  5.7M  506M   2% /boot/efi
> tmpfs           100K     0  100K   0% /var/lib/lxd/shmounts
> tmpfs           100K     0  100K   0% /var/lib/lxd/devlxd
> root@server:~#
> 
> Is it exact ?

   Yes, it looks like you're running / from the FS on /dev/sda2.

> If yes, I suppose I should wipe data on /dev/sdb, then build the
> RAID by expanding /dev/sda2.

   Correct.

   I would recommend putting a partition table on /dev/sdb, because it
doesn't take up much space, and it's always easier to have one already
there when you need it (and there's a few things that can get confused
if there isn't a partition table).

> So I should :
> 
> wipefs /dev/sdb
> btrfs device add /dev/sdb /
> btrfs balance start -v -mconvert=raid1 -dconvert=raid1 /

> Does it sound correct ? (my kernel is boot/vmlinuz-4.18.0-1-amd64)

   Yes, exactly.

   Hugo.

-- 
Hugo Mills             | Yes, this is an example of something that becomes
hugo@... carfax.org.uk | less explosive as a one-to-one cocrystal with TNT.
http://carfax.org.uk/  | (Hexanitrohexaazaisowurtzitane)
PGP: E2AB1DE4          |                                            Derek Lowe

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