> In my experience, "hung task" is almost always due to running out of RAM

In my case, I don't think this machine ever commits more than around 5GB of its 32GB available memory, so I doubt it's that.

> it also seems common for people to completely disregard the well-documented "this feature is unreliable, don't use it" warnings that btrfs has

Now that I am definitely doing. I won't give up raid6 until it eats all my data for a fourth time.