Re: rw-mount-problem after raid1-failure

[Martin <develop@imagmbh.de>]

Hello Anand,

the failed disk was removed. My procedure was the following:

 - I found some write errors in the kernel log, so
 - I shutdown the system
 - I removed the failed disk
 - I powered on the system
 - I mounted the remaining disk degraded,rw (works OK)
 - the system works an and was rebooted some times, mounting degraded,rw works
 - suddentlym mounting degraded,rw stops working and only degraded,ro works.

Thanks, Martin


Am Mittwoch, 10. Juni 2015, 15:46:52 schrieb Anand Jain:
> 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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