19.09.2017 14:49, Senén Vidal Blanco пишет:
> Perfect!! Just what I was looking for.
> Sorry for the delay, because before doing so, I preferred to test to see if it 
> actually worked.
> 
> I have a doubt. The system works perfectly, but at the time of deleting the 
> writing disk and merging the data on the read-only disk I fail to understand 
> the process.
> 
> I have tried to remove the seed bit on disk A and delete the write B as you 
> mention, and so move the data to A, but tells me that disk B does not exist.
> These are the orders I have made:
> 
> md127-> A
> md126-> B
> 
> btrfstune -S 0 /dev /md127
> mount /dev/md127 /mnt (I mount this disk since the md126 gives error)
> btrfs device delete /dev/md126 /mnt
> ERROR: error removing device '/dev/md126': No such file or directory
> 
> Another thing I've tried is to remove disk B without removing the seed bit, 
> but it gives me the error:
> 
> ERROR: error removing device '/dev/md126': unable to remove the only writeable 
> device.
> 
> Any ideas about it?

Yes, sorry about it. Clearing seed flag on device invalidates
filesystem. What you can do, is to rotate devices. I.e. remove
/dev/md126, set seed flag on md127 and add md126 back.

I actually tested it and it works for me.

> Thank you very much for the reply.
> Greetings.
> 
> El martes, 12 de septiembre de 2017 6:34:15 (CEST) Andrei Borzenkov escribió:
>> 11.09.2017 21:17, Senén Vidal Blanco пишет:
>>> I am trying to implement a system that stores the data in a unit (A) with
>>> BTRFS format that is untouchable and that future files and folders created
>>> or modified are stored in another physical unit (B) with BTRFS format.
>>> Each year the new files will be moved to store A and start over.
>>>
>>> The idea is that a duplicate of disk A can be made to keep it in a safe
>>> place and that the files stored there can not be modified until the
>>> mixture of (A) and (B) is made.
>>
>> This can probably be achieved using seed device. Mark original device as
>> seed and all changes will go to another writable device, similar to
>> overlay; then remove seed bit from original device, "btrfs device remove
>> writable" device and it should relocate its content back. Rinse and repeat.
>