Re: Storage and snapshots as historical yearly

["Senén Vidal Blanco" <senenvidal@sgisoft.com>]

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

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.

> > 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.

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	Senén Vidal Blanco - SGISoft S.L.
 
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