XigmaNAS

Seagate NAS HDD 4TB is 4K physical emulated at 512-byte sectors (according to its manual)

This blog (http://nex7.blogspot.com.br/2013/03/readme1st.html) states that

The problem is a number of these devices are lying to the OS about their sector size, claiming it is 512-byte; this will cause significant performance issues if not dealt with at zpool creation time.

My question is: What should be done at the zpool creation time?

Check the force 4k sectors box on N4F.

Step by step How-to (use your own pool names etc, ZFS format, etc. examples are my own server)
1st: Disks=>Format. Select the 1st disk: da0 for example. Select file system: ZFS Storage pool device. format. repeat for all disks of your pool.
2nd: Disks=>ZFS=>Pools=>Virtual device. Click Add device. Name: virtual_device1. Type: Double-parity Raid-Z. Devices: select all that will be part of this pool. Select: Enable Advanced Format (4KB sector)
Click "ADD" and then click "Apply changes".
3rd: now you can proceed to create your pools.