Re: rw-mount-problem after raid1-failure

[Anand Jain <anand.jain@oracle.com>]

On 06/10/2015 02:58 PM, Martin wrote:
> Hello Anand,
>
> the
>
>> mount -o degraded <good-disk> <-- this should work
>
> is my problem. The fist times it works but suddently, after a reboot, it fails
> with message "BTRFS: too many missing devices, writeable mount is not allowed"
> in kernel log.

  the failed(ing) disk is it still physically in the system ?
  when btrfs finds EIO on the intermittently failing disk,
  ro-mode kicks in, (there are some opportunity for fixes which
  I am trying). To recover, the approach is to make the failing
  disk a missing disk instead, by pulling out the failing disk
  from the system and boot. When system finds disk missing
  (not EIO rather) it should mount rw,degraded (from the VM part
  at least) and then replace (with a new disk) should work.

Thanks, Anand


> "btrfs fi show /backup2" shows:
> Label: none  uuid: 6d755db5-f8bb-494e-9bdc-cf524ff99512
> 	Total devices 2 FS bytes used 3.50TiB
> 	devid    4 size 7.19TiB used 4.02TiB path /dev/sdb2
> 	*** Some devices missing
>
> I suppose there is a "marker", telling the system only to mount in ro-mode?
>
> Due to the ro-mount I can't replace the missing one because all the btrfs-
> commands need rw-access ...
>
> Martin
>
> Am Mittwoch, 10. Juni 2015, 14:38:38 schrieb Anand Jain:
>> Ah thanks David. So its 2 disks RAID1.
>>
>> Martin,
>>
>>    disk pool error handle is primitive as of now. readonly is the only
>>    action it would take. rest of recovery action is manual. thats
>>    unacceptable in a data center solutions. I don't recommend btrfs VM
>>    productions yet. But we are working to get that to a complete VM.
>>
>>    For now, for your pool recovery: pls try this.
>>
>>       - After reboot.
>>       - modunload and modload (so that kernel devlist is empty)
>>       - mount -o degraded <good-disk> <-- this should work.
>>       - btrfs fi show -m <-- Should show missing if you don't let me know.
>>       - Do a replace of the missing disk without reading the source disk.
>>
>> Good luck.
>>
>> Thanks, Anand
>>
>> On 06/10/2015 11:58 AM, Duncan wrote:
>>> Anand Jain posted on Wed, 10 Jun 2015 09:19:37 +0800 as excerpted:
>>>> On 06/09/2015 01:10 AM, Martin wrote:
>>>>> Hello!
>>>>>
>>>>> I have a raid1-btrfs-system (Kernel 3.19.0-18-generic, Ubuntu Vivid
>>>>> Vervet, btrfs-tools 3.17-1.1). One disk failed some days ago. I could
>>>>> remount the remaining one with "-o degraded". After one day and some
>>>>> write-operations (with no errrors) I had to reboot the system. And now
>>>>> I can not mount "rw" anymore, only "-o degraded,ro" is possible.
>>>>>
>>>>> In the kernel log I found BTRFS: too many missing devices, writeable
>>>>> mount is not allowed.
>>>>>
>>>>> I read about https://bugzilla.kernel.org/show_bug.cgi?id=60594 but I
>>>>> did no conversion to a single drive.
>>>>>
>>>>> How can I mount the disk "rw" to remove the "missing" drive and add a
>>>>> new one?
>>>>> Because there are many snapshots of the filesystem, copying the system
>>>>> would be only the last alternative ;-)
>>>>
>>>> How many disks you had in the RAID1. How many are failed ?
>>>
>>> The answer is (a bit indirectly) in what you quoted.  Repeating:
>>>>> One disk failed[.] I could remount the remaining one[.]
>>>
>>> So it was a two-device raid1, one failed device, one remaining, unfailed.
>>
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