Re: Cannot 'mount -o degraded /dev/replacement' after a replace

[Qu Wenruo <quwenruo.btrfs@gmx.com>]

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On 2019/2/9 下午6:36, Jakob Schöttl wrote:
> Hi,
> 
> I've setup a RAID1 with two disks (disk1 and disk2) and I'm testing the
> btrfs replace command.
> 
> After replacing disk2 with disk3, I can only mount
> (a) disk1 or disk3 (if both disk are plugged) and
> (b) the original disk1 (degraded, if disk3 is unplugged).
> 
> I cannot mount the replacement disk3 if disk1 is unplugged.

Sounds like there is one single chunk on disk1, which caused the problem.

> 
>> mount: /mnt: wrong fs type, bad option, bad superblock on /dev/loop3,
> missing codepage or helper program, or other error.

dmesg please.

And btrfs-progs version please.

Maybe mkfs is too old to leave SINGLE profile chunks on the original fs.

And you could verify the chunk mapping by executing 'btrfs ins dump-tree
-t chunk <device>' and paste the output.

Thanks,
Qu

> 
> What I expect is that both disk1 and disk3 are fully valid and working
> after a replace.
> 
> Steps to reproduce:
> 
>   dd if=/dev/zero of=/vdisk1 bs=1024 count=300000
>   losetup /dev/loop1 /vdisk1
>   dd if=/dev/zero of=/vdisk2 bs=1024 count=300000
>   losetup /dev/loop2 /vdisk2
>   dd if=/dev/zero of=/vdisk3 bs=1024 count=300000
>   # losetup /dev/loop3 /vdisk3    # don't plug this device yet
> 
> Create RAID1 file system:
> 
>   mkfs.btrfs -L datavol -m raid1 -d raid1 /dev/loop1 /dev/loop2
> 
> Unplug device 2 to simulate a defect:
> 
>   losetup -d /dev/loop2
> 
> Plug device 3:
> 
>   losetup /dev/loop3 /vdisk3
> 
> Replace device 2 with device 3:
> 
>   mount -o degraded /dev/loop1 /mnt
>   btrfs filesystem show   # to get devid of device 2
>   btrfs replace start -Br 2 /dev/loop3 /mnt
>   btrfs replace status /mnt   # check success
>   umount /mnt
> 
> Unplug the original device 1 to see if device 3 has really replaced
> device 2:
> 
>   losetup -d /dev/loop1
>   mount -o degraded /dev/loop3 /mnt
> 
> The mount fails with this error:
> 
>> mount: /mnt: wrong fs type, bad option, bad superblock on /dev/loop3,
> missing codepage or helper program, or other error.
> 
> In this situation, btrfs device scan does not change anything and btrfs
> filesystem show shows:
> 
>> warning, device 1 is missing
>> warning, device 1 is missing
>> warning, device 1 is missing
>> warning, device 1 is missing
>> bad tree block 198180864, bytenr mismatch, want=198180864, have=0
>> ERROR: cannot read chunk root
>> Label: 'datavol'  uuid: 640e45d3-e741-4a78-a24e-2d8a41c6b8c3
>>     Total devices 2 FS bytes used 128.00KiB
>>     devid    2 size 292.97MiB used 104.00MiB path /dev/loop3
>>     *** Some devices missing
> 
> Is this a known problem? Can you reproduce it? Am I doing something wrong?
> 
> Regards, Jakob
> 


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