Filesystem creation and checking time
The first test is related to filesystem creation and checking times. The following graph will show you the time needed to create and fsck the ~16 TB (~14.5 TiB) filesystem used to fill the RAID 6 array. The fsck command was run after the creation of a significant number of small files, obtained unpacking the linux-188.8.131.52.tar.bz2 file downloaded form kernel.org:
As you can see, XFS was way faster then EXT4 in creating the volume, while EXT4 is the winner in fsck operation. However, remember that you generally create the filesystem only one time, and the fsck operation should be a rare one (after all, both FS are journaled for this reason). On the other hand, if you plan to often create a large filesystem, stay away from EXT4 and go with XFS.