In many systems the bottleneck is writing not reading. For example in a typical mail server writes will outnumber reads because if you have adequate cache then most mail is read from cache as the users who poll mail the most frequently tend to be the ones who receive the most mail. When writes are the bottleneck you don't want to do much to defragment disk allocation which is good for reads. You want to interleave writes for multiple files to defragment writes. WAFL, ZFS, and I believe BTRFS do this. Automatic defragment on BTRFS is new and experimental, I won't use it for a while except on the most experimental systems. Also I think that the balance bug that affects systemd systems would also get autodefragment. -- Sent from my Samsung Galaxy Note 2 with K-9 Mail.