ReiserFS was all that for a hot minute, but once tailpacking killed some files in /etc after a crash I never went back; XFS was a bit slower but way more reliable.
And no wife murder.
And no wife murder.
There is no upgrade to the new format; they must be dumped and reloaded.
I'm sorry if this is you. I don't think there are any upgrade paths.
Edit: I see that V5 is the upstream default since "only" ~2015, so indeed there are likely many V4 filesystems still around.