We have this setup on our server:Ubuntu 14.04 (used to be 12.04)10TB RAID-6 system LVM (one VG, two LV)ext4 partition ( ~2TB)Btrfs partition ( ~8TB)After a reboot last month the system was slow. First we thought it was because the RAID was resyncing (one drive was not added and was reactivated). But after that finally finished (12-13 days) access to Btrfs still is noticably slow. ext4 access seems normal.The sysadmin who set this up (and who left this summer) already used autodefrag,noatime on the Btrfs mount.What can we do to get Btrfs speed up again? 
Slow access to btrfs on LVM/
lvm;btrfs
I can't comment, sorry if this is not good as answer. You should check your drives. I think 12 days of rsync time for 10Tb is too long, should be more like 12-24 hours. Look at the different drives with smartctl to check if one has many errors: for i in a b c d e f g h i j k l; do echo $i ; smartctl -x /dev/sd$i | grep occurred | head -1 ; doneI have seen working RAID slow down because of this. And IIRC Btrfs needs more disc access than ext4 for directory look ups, which could explain access speed difference.