I happen to have the troff source for some version of the XFS usenix paper as I was a reviewer (I think, maybe it was that I formatted it because I was troff nerd).
The online fsck support looks really cool. We use XFS at work because Ext4 has issues dealing with too many files. Anyone else use XFS for other reasons ?
It is a default for RHEL7/CentOS7, so I imagine many people use it.
XFS Project Quotas -- quotas enforced on write without requiring traditional users to be set up.
Handy for untrusted Docker containers which need to run as one UID but still want per-container quotas.
These days, ext4 has project quota support, too.
Hands down best in sequential write performance.
We ran into problems with ext4 on an NFS server with 64-bit inodes and 32-bit clients. XFS had a mount option that solved it. We're likely to stick with it now as we prefer the quotas.
Large changes to filesystem drivers make me nervous. I will be giving this 6-12 months to bake before putting it anywhere near important systems. That said, XFS is great and I do look forward to using the improvements.
Can someone give me an "explain like i'm five" high level view of why i would want to use XFS over Ext4 or the pros and cons between the two?