btrfs metadata mirroring

btrfs metadata mirroring

[Zener]

Hi, I have a disk with btrfs but now I'd like enable just metadata 
mirroring to understand if some error occurs.
Do I need another disk / partition / volume dedicated?
How to do?
Is it safe now or do I risk to loss my formely data?
Thank you for your support.
Bye.

Re: btrfs metadata mirroring

[Hugo Mills]

On Fri, Nov 27, 2020 at 04:11:19PM +0100, Zener wrote:
> Hi, I have a disk with btrfs but now I'd like enable just metadata mirroring
> to understand if some error occurs.
> Do I need another disk / partition / volume dedicated?
> How to do?
> Is it safe now or do I risk to loss my formely data?

   It's quite possible that you already have it.

   If you look at the output of "btrfs fi usage -T /mountpoint",
you'll see the RAID level for your metadata listed. If it's "DUP",
then you have two copies of each metadata block duplicated --
effectively running "RAID-1" for your metadata, but on a single
device.

   If it says "single", then you've only got one copy of your
metadata. You can convert it to DUP with a balance conversion:

# btrfs balance start -mconvert=dup,soft /mountpoint

   You may need to run this more than once. Sometimes the conversion
process manages to allocate (and then skip over) a new metadata chunk
as single. Check with "btrfs fi usage -T /mountpoint" after running
the first time, and see if there's any single metadata allocation
left. If there is, run the command again.

   Hugo.

-- 
Hugo Mills             | Anyone who says their system is completely secure
hugo@... carfax.org.uk | understands neither systems nor security.
http://carfax.org.uk/  |
PGP: E2AB1DE4          |                                        Bruce Schneier