This document explains how to add iSCSI storage to second ESXi host after you already created a data store on the first ESXi host.
1. From the vSphere client, go to Configuration and Storage Adapters. If you do not see the iSCSI adapter already installed, click on Add button to add the software iSCSI adapter.
2. Choose the Add Software iSCSI Adapter.
3. Right click on the newly created iSCSI Software Adapter and click Properties.
4. Click on Dynamic Discovery tab.
5. Type the iSCSI server IP address. That is the IP address of your NAS device. Once the NAS is registered, you can run Rescan All from the Main screen.
If all goes well, you will see the NAS show up under the iSCSI Adapter screen.
6. From the Configuration screen, now go to Storage screen. Click Rescan All button, and you should see the Data Storage show up on the list.
If you do not see the Data Storage after you completed the step 6, you may need to manually mount the data storage. See https://akhpark.wordpress.com/2013/12/05/cannot-add-vmfs-datastore-to-esxi-host-only-gives-option-to-format-a-new-drive/ for more information.