Which device is missing ?

Which device is missing ?

[Pierre Couderc]

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

root@server:~# fdisk -l
Disk /dev/sda: 1.8 TiB, 2000398934016 bytes, 3907029168 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: gpt
Disk identifier: CFF97102-D6B5-4126-B2B4-FA735598D1F0

Device       Start        End    Sectors  Size Type
/dev/sda1     2048    1050623    1048576  512M EFI System
/dev/sda2  1050624 3907026943 3905976320  1.8T Linux filesystem


Disk /dev/sdb: 1.8 TiB, 2000398934016 bytes, 3907029168 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 4096 bytes
I/O size (minimum/optimal): 4096 bytes / 4096 bytes


root@server:~# btrfs fi usage /
Overall:
     Device size:                   1.82TiB
     Device allocated:            196.02GiB
     Device unallocated:            1.63TiB
     Device missing:                  0.00B
     Used:                        191.84GiB
     Free (estimated):              1.63TiB      (min: 835.27GiB)
     Data ratio:                       1.00
     Metadata ratio:                   2.00
     Global reserve:              263.64MiB      (used: 0.00B)

Data,single: Size:192.01GiB, Used:189.98GiB
    /dev/sda2     192.01GiB

Metadata,DUP: Size:2.00GiB, Used:951.67MiB
    /dev/sda2       4.00GiB

System,DUP: Size:8.00MiB, Used:48.00KiB
    /dev/sda2      16.00MiB

Unallocated:
    /dev/sda2       1.63TiB
root@server:~#

Re: Which device is missing ?

[Hugo Mills]

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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*

   Hugo.

[snip]

-- 
Hugo Mills             | UNIX: Japanese brand of food containers
hugo@... carfax.org.uk |
http://carfax.org.uk/  |
PGP: E2AB1DE4          |

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Re: Which device is missing ?

[Hugo Mills]

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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.

-- 
Hugo Mills             | Welcome to Rivendell, Mr Anderson...
hugo@... carfax.org.uk |
http://carfax.org.uk/  |
PGP: E2AB1DE4          |                            Machinae Supremacy, Hybrid

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Re: Which device is missing ?

[Pierre Couderc]

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

Re: Which device is missing ?

[Hugo Mills]

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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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Re: Which device is missing ?

[Pierre Couderc]

On 10/08/2018 11:21 PM, Hugo Mills wrote:
> 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.
>
Thnk you very very much.
I do it now, as you with a partition table on /dev/sdb !

merge status of per-chunk degradable check [was Re: Which device is missing ?]

[Nicholas D Steeves]

[-- Attachment #1: Type: text/plain, Size: 1843 bytes --]

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 :
[...]
>    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*

I think this was the patch that addressed this?:
  https://www.spinics.net/lists/linux-btrfs/msg47283.html
  https://patchwork.kernel.org/patch/7226931/

In my notes it wasn't present in <= 4.14.15, but my notes might be
wrong.  Does this patch resolve the one-shot -o degraded, reboot,
forever read-only behaviour, or is something else required?  When was
it merged?  Has it been or will it be backported to 4.14.x?  I'm
guessing 4.9.x is too far back, but it would be really nice to see it
there too :-)

Also, will this issue be resolved for linux-4.19?  If so I'd like to
update the Debian btrfs wiki with this good news :-)

Finally, is the following a valid workaround for users who don't have
access to a kernel containing this fix:

1. Make a raid1 profile volume (both data and metadata) with >= 3 disks.
2. Lose one disk.
3. Allocator continues to write raid1 chunks instead of single,
because it is still possible to write one chunk to two disks.
4. Thus reboot twice -> forever read-only averted?


Kind regards,
Nicholas

P.S. Please let me know if you'd prefer for me to shift this
documentation effort to btrfs.wiki.kernel.org.

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Re: merge status of per-chunk degradable check [was Re: Which device is missing ?]

[Hans van Kranenburg]

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On 10/09/2018 02:08 AM, Nicholas D Steeves 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 :
> [...]
>>    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*
> 
> I think this was the patch that addressed this?:
>   https://www.spinics.net/lists/linux-btrfs/msg47283.html
>   https://patchwork.kernel.org/patch/7226931/
> 
> In my notes it wasn't present in <= 4.14.15, but my notes might be
> wrong.  Does this patch resolve the one-shot -o degraded, reboot,
> forever read-only behaviour, or is something else required?  When was
> it merged?  Has it been or will it be backported to 4.14.x?  I'm
> guessing 4.9.x is too far back, but it would be really nice to see it
> there too :-)
> 
> Also, will this issue be resolved for linux-4.19?  If so I'd like to
> update the Debian btrfs wiki with this good news :-)

[...]

> P.S. Please let me know if you'd prefer for me to shift this
> documentation effort to btrfs.wiki.kernel.org.

Yes, absolutely. This is not specific to how we do things for Debian.
Upstream documentation can help all distros.

-- 
Hans van Kranenburg


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