Is it safe to use btrfs with a 4.9 kernel or should I use the latest kernel?
You shouldn't use btrfs, regardless of the kernel version.
>>61750513
What is a good FS for root? btrfs gives me snapshots in case something goes wrong.
>>61750496
Stable should be fine, but even Ubuntu LTS is on mainline 4.10.
Kernel 5.0 or iPhone 8???