Prior to 2.6.26 fuse only supported single page write requests. In theory all
fuse filesystem should be able support bigger than 4k writes, as there's
nothing in the API to prevent it. But there was a known case in ntfs-3g
which caused corruption while using earlier fuse so they disabled bigger
than 4kb writes by default since 2.6.26. But there is an option to use
it for filesystems which can handle it i.e -obig_writes as fuse opt args.
So as earlier fuse 2.7.x and direct-io disabled glusterfs used to
receive 4kb chucks at all times resulting in applications writing at
bigger block sizes crunch with slower performance. But big_writes will
be enabled by default in glusterfs if you use fuse-2.8.0 even if you use
disable-direct-io or not.