Mounting a RAID 1 in degraded mode

Mounting a RAID 1 in degraded mode

[Tobias Kronawitter]

Hi

I fooled around with RAID and didn't quite get how to use -o degraded
the way it's meant. I asked on
http://askubuntu.com/questions/49893/how-does-btrfs-raid-work-in-degraded-mode/
. It goes like this:
-Create the raid array "sudo mkfs.btrfs -m raid1 -d raid1 /dev/loop1 /dev/loop2"
-mount them "sudo mount /dev/loop1 /mnt" and mark them "touch goodcondition"
-You unmount and simulate disk failure (remove disk or delete loopback
device loop2 in my case)
-You mount degraded "-o degraded" and mark again "touch degraded"
-You add the bad disk again "sudo btrfs dev add /dev/loop2"
-You rebalance "sudo btrfs fi ba /mnt"
And Raid 1 should work again. But that's not the case. "sudo btrfs fi show":

Total devices 3 FS bytes used 28.00KB
devid    3 size 4.00GB used 264.00MB path /dev/loop1
devid    2 size 4.00GB used 272.00MB path /dev/loop2
*** Some devices missing

It looks like I added another device instead of replacing.
I got the info so far from
https://btrfs.wiki.kernel.org/index.php/Using_Btrfs_with_Multiple_Devices#Creating_a_Multi-device_FS
last paragraph.

So howdo I tell btrfs to use the newly created loop2 as a replacement for loop2

NB This is the first time I'm using a mailing list, so if I'm making
some obvious mistakes please point them out.

Tobias Kronawitter

Re: Mounting a RAID 1 in degraded mode

[Miguel Garrido]

On Wed, Jun 22, 2011 at 7:15 AM, Tobias Kronawitter
<tobias.kronawitter@tuhh.de> wrote:
>
>
> It looks like I added another device instead of replacing.
> I got the info so far from
> https://btrfs.wiki.kernel.org/index.php/Using_Btrfs_with_Multiple_Devices#Creating_a_Multi-device_FS
> last paragraph.
>

Take a look a the "Replacing Failed Devices" section of that page.

It is possible if you created a brand new loop device that it was
picked up as a different disk altogether by btrfs (different unique
ID) so you need to delete the missing disk from the volume and then
rebalance.

At least that is my understanding of how it is supposed to work.

--
MG