Oracle Database is not certified to run on either btrfs or ZFS on Linux, so if 

certification is an issue, you can't use either filesystem. 

Right, I had missed that - only ZFS on Solaris is officially supported I 
suppose. We had to draw the line somewhere, and an Oracle OS with an Oracle 
database with an Oracle filesystem seemed like a good platform. If the BTRFS 
pieces are indeed a year old in the latest official binary kernel from last 
month, that just makes me wonder why Oracle didn't use these latest bits. 
Again, I'm inclined to think we're dealing with a design difference between 
ZFS and BTRFS rather than a missing performance optimization. You'd know that 
better than I. :)

Out of interest, have you done a performance benchmark with ASM using ASMlib
on the same platform? 

Sorry, no. Our experience with ASM is limited, we came to the conclusion once
that we like being able to handle the files in a plain mountable file-system.