A ODROID forum user @linuxest reported the most affordable 8TB external storage could work with XU4 UAS driver in Kernel 4.9.

I also wanted to make my own NAS because my Google Cloud storage was almost full.
I ordered the same storage(STEB8000100) from Amazon. It is US$180 only. 1TB costs $22 approximately.
https://www.amazon.com/Seagate-Expansion-Desktop-External-STEB8000100/dp/B01HAPGEIE

It has arrived here this morning and I have run a few samba performance test with kernel 4.9 on my xu4q. I formatted the storage with EXT4 file system before testing because its stock file system is NTFS.

Downloading an 8GB file to my laptop from the XU4 NAS. It shows 110MB/sec of transfer speed stably.

Uploading an 8GB file to the XU4 NAS from my Windows laptop. It shows 90~100MB/sec of transfer speed.

Helios LanTest (3GB transfer option) also shows good performance too.

How to Assemble !

XU4Q and the official case

Velcro tape (3M Scotch 40mm x 25mm 4-pairs)

Attach Velcro tape (loop side) to the XU4Q case bottom

Attach Velcro tape (hook side) to the Seagate HDD case

Place the XU4Q case on the HDD case

Connect cables.
DC plug for HDD, DC plug for XU4Q, Ethernet and USB 3.0 cables.

Hardkernel announced the Linux kernel 4.9.11 support for the ODROID-XU4 and XU3 platforms in late February and we started a debugging party. After ten weeks of debugging party with our community members, we are proudly releasing a new Ubuntu image based on latest Linux kernel 4.9.27 LTS.

Hardkernel proudly announces the Linux kernel 4.9 release for the ODROID-XU4 and XU3 platforms.
This LTS(Long Term Support) kernel 4.9 will be actively updated until early 2019.

Key features of the XU4 hardware are working on kernel 4.9.11 as of today.
Cortex-A15/A7 Octacore HMP, HDMI video and audio, USB 3.0, Gbit Ethernet, Mali-T628MP6 GPU, MFC VPU and eMMC HS400 mode are functional now.

There are tons of commits, patches and merges done for the last few months.
Grab the source code from our kernel 4.9 Github branch.

We must say that Samsung OSG(Open Source Group) helped a lot to make the dream comes true.
They contributed 394 patches that modified 15,856 lines of code in kernel 4.9 tree.

We invite you to a Debugging Party in our community forum. We will pull your ideas, comments and applause.
Try and verify Ubuntu 16.04.2 Mate image which launches the kernel 4.9.11 in that forum too.