On 2015-08-05 22:13, Chris Murphy wrote:
> On Wed, Aug 5, 2015 at 6:45 PM, Paul Jones <paul@pauljones.id.au> wrote:
>> Would it be possible to store this type of critical information twice on each disk, at the beginning and end? I thought BTRFS already did that, but I might be thinking of some other filesystem. I've had my share of these types of oops! moments as well.
>
> That option is metadata profile raid1. To do an automatic
> -mconvert=raid1 when the user does 'btrfs device add' breaks any use
> case where you want to temporarily add a small device, maybe a USB
> stick, and now hundreds of MiBs possibly GiBs of metadata have to be
> copied over to this device without warning. It could be made smart,
> autoconvert to raid1 when the added device is at least 4x the size of
> metadata allocation, but then that makes it inconsistent. OK so it
> could be made interactive, but now that breaks scripts. So... where do
> you draw the line?
>
> Maybe this would work if the system chunk only was raid1? I don't know
> what the minimum necessary information is for such a case.
>
> Possibly it make more sense if 'btrfs device add' always does
> -dconvert=raid1 unless a --quick option is passed?
>
Perhaps we could print out a big noisy warning that could be silenced?