For this one I used, in terms of:

• hardware:
  • SuperMicro SuperServer SYS–E300-8D
  • QNAP TS-563 (4.2.2 Build 20160823) AMAZON ref. link
  • Netgear ProSafe GS108Tv2 (Boot Version B5.1.0.2 Software version 5.4.2.22) AMAZON ref. link
• software
  • ESX 6.0 (VMware-VMvisor-Installer-6.0.0.update02-3620759.x86_64)
  • vCenter 6 (VMware-VIMSetup-all-6.0.0-3634788)

• log in to admin UI of the switch
• go to Switching / VLAN
• fill in the field under VLAN ID and VLAN Name
• click on Done (bottom of the screen)
• newly added entry show be listed now
• go to Switching / VLAN / Advanced / VLAN Membeship
• select previously configured VLAN ID from the droplist
• click on PORT and select which port you’d like to assign this VLAN (after you select the port it’s either T(agged) or U(untagged), in my case I will be using Tagged on port 4 and 5
• once done click on Apply (bottom of the screen)

In my case I’m using QNAP NAS which has 2 network interfaces:

• 1st is for general access and applications
• 2nd is for iSCSI
  • make sure the iSCSI service in running on the interface
  • also you can enable jumbo frames (I chose MTU of 9000) System Settings / Network / Network & Virtual Switch / Intefaces / [Interface] and edit:
  • configure storage pool (RAID_what_ever_you_like), I used just one disk because I can
  • go to Storage Manager / iSCSI / iSCSI Storage, if you are doing it for the first time you’ll see the the following popup (click on Yes)
  • select 1st option – iSCSI Target with a mapped LUN and click on Next
  • click on Next
    
  • name the target and check all optional CRC/Checksum items, click on Next
  • I skipped configuring MSCHAP, so if you feel the same way just click on Next
  • since I’m using single volume I select first checkbox, for your production needs make sure you select the second one which points to the storage pool, click on Next
  • since I’m all about speed I selected Instant Allocation, capacity was “Set to Max”; from Advanced settings I did not checked 4K because it doesn’t work with my current build of ESX but no problems with Report volatile… and FUA bit. Click on Next 
  • if you like what you see click on Next if not go back and amend
  • click on Finish
  • now you configured the iSCSI target, by clicking on arrow on the left to LUN0 you will see a iSCSI LUN already mapped to the target
  • as a optional step you may want to configure iSCSI ACL (see the button), since I use the following default policy
  • which is basically R/W to the LUN
  • one last thing I did was to set up iSNS for easy discovery, click on Settings
  • check the checkbox and type in the IP (same as the one that is bound to iSCSI service) and click on Apply

• head on over to the vSphere side of things (I use vCenter) to configure iSCSI adapter, mount the LUN and create a datastore over iSCSI
• I’m using HTML (almost) Web Client

• go to Hosts and Clusters / [select the ESXi] / select Manage then Networking then Virtual Switch and Click on Add host netwroking
• select VMkernel Network Adapter
• select New standard switch
• select Add adapters
• select the NIC that has connection to the iSCSI VLAN, in my case it was vmnic2
• review and click on Next
• name it and provide VLAN ID, click on Next
• address the NIC in order to have L3 connectivity with a iSCSI service hosted on QNAP, click on Next
• review if fine then click on Finish
• edit the newly created vSwitch 
• type in the MTU size, in my case I used 9000 then click on OK
• on the same vswitch click on vmk and select edit
• from the NIC settings type in MTU size and click on OK
• select storage under Manage Tab and click on Add new storage adapter 
• select iSCSI adapter 
• click on OK 
• you should see new Storage adapter, if not click on this refresh icon located on the top 
• once selected just below you should see the details, the adapter should be enabled
• select Network Port Binding, you should see here a iSCSI port group 
• select Targets, since I enabled autodiscovery on the QNAP it was discovered on ESXi just fine
• go to Advanced Options and make sure Header and Data Digest options are Preffered if not Edit them
• head back to Home and select Storage
• then pick either Datacenter or Cluster object; from Actions drop menu select  Storage and New datastore
• click on Next
• select VMFS
• you should see you LUN presented, select it, name it and click on Next
• if you don’t see it click on Cancel and select Actions – Storage – Rescan Storage and then scan for both Storage Devices and VMFS Volumes
• I’m using all space on the LUN so I just click on ok
• review if fine then confirm by clicking on Finish
• the datastore is defined, formatted and usable, congratulations