Ask HN: Which disk defragmentation algorithms are used in major OS?
Which algorithms are used to make disk defragmentation on OS X, Windows, and some Linux distro?
XFS and ext4 will online defrag, i.e. when your volume is les than 90% full you don't worry about it, if its fuller than that fragmentation is not the problem to worry about.
BTRFS and other COW fragment easily but advantage means fragmentation is not your prime concern. Also large single write files are not the problem. When using NOCOW on a directory see above.
MAC OS X you will have terrible performance anyway... Relatively speaking if you have more than 2 disks per volume.
Windows... no idea to be honest