El martes, 19 de septiembre de 2017 21:33:31 (CEST) Andrei Borzenkov escribió:

19.09.2017 14:49, Senén Vidal Blanco пишет:

quoted

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.

OK thanks

Now I see how it works :))

With the commands:
mount /dev/md126 /mnt
btrfs device remove /dev/md127 /mnt
We remove the read-only array (A) from the BTRFS system and in doing so pass 
all the information from (A) to (B) read-write to mix them.

From what I see is not bad since both (A) and (B) are still operational. (A) 
with last year and (B) with everything current.

Finally with this other commands:
btrfstune -S 1 /dev/md126
mount /dev/md126 /mnt
btrfs device add -f /dev/md127 /mnt
we activate the seed bit in md126 (B) and add the (A) in read-write mode, 
where the new files will be archived and (B) as store until the following year 
and (A) do clean to fill in it new data.

I have tried to rotate twice to see if it goes well and smoothly.

Just comment that I see two small problems to this:

1. The transfer of data from (A) to (B) when removing the read-only disk takes 
quite a while and more the more it has stored in the history. It would be nice 
if the process were reversed, since in (B) there are fewer "data" stored. 
Also, I could not use it monthly or daily for this reason.

2. My idea was to have a larger A-disk than B where I would save the 
historical ones, because so in B I could put a smaller disk and something 
faster. If the decoupling process outside read-write rather than read-only and 
passed the data to A would be ideal for this case.

On the other hand, as an anecdote only, and perhaps for lack of experience or 
knowledge, I have used the entire linux system in BTRFS (@ and @home) format 
and a single partition md126 to have the system bootable and running simply by 
attaching the disk to the computer in degraded mode (swap outside the raid , 
which I'm not so bad: P). This has made that by rotating disks A and B I have 
had some problems with grub and fstab at boot, which I had to overcome by 
making changes to the boot configurations and some more botches.

I'm going to see a couple more things and if there's any way I can combine 
this with snapshots and see if the bulb will light up. If I do not get it I 
will try with the other filesystems that you have suggested to me. Although 
honestly, I like BTRFS more than the other alternatives, I already use BTRFS 
on 5 computers and it goes very well.

Greetings.

quoted

Thank you very much for the reply.
Greetings.

El martes, 12 de septiembre de 2017 6:34:15 (CEST) Andrei Borzenkov 

escribió:

quoted

quoted

11.09.2017 21:17, Senén Vidal Blanco пишет:

quoted

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.

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