On 3 Sep 2017 21:23, "Russell Coker via luv-main" <luv-main@luv.asn.au> wrote:

It turned out to be BTRFS mis-managing free space, deciding there was none left, and going into read-only mode.

I've been burnt by this too, on a desktop. I think you need to watch both btrfs fi show and btrfs df.