Ceph

I expect others to improve this list, but to start it out ...

what file systems we run on (and test on)

how you can make the right trade-off in deciding which to use

how easy it is to change your decision later

btrfs
how it improves our performance
value (and limitations) of checksumming
observed issues and our expectations

xfs
advantages over btrfs
performance issues vs btrfs, why it has them

ext4
advantages over btrfs
performance issues vs btrfs, why it has them