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Configure iSCSI LUNs on Synology NAS

Synology NAS Configuration

I recently purchased a 4 bays Synology NAS and apart from the initial excitement about the new toy this is something I was looking forward to enhance my lab environment using a physical storage. I decided to go with four Western Digital RED Pro 3TB drives. At the beginning I was personally debated between RAID 5 vs. RAID 10. Using a RAID 5 I could get a whopping 9TB (with 1 drive reserved for protection) and high throughput for READs. Choosing a RAID 10 gives me 6TB (stripe + mirror) and higher performances with WRITEs. Although it is true I won’t be hosting highly-intensive Databases it also true I don’t currently need 9TB of storage either. So purely from a curiosity perspective about the performances I opted for a RAID 10.

The purpose of this article is to show the steps required to configure a LUN with an iSCSI Target using a Synology NAS. This article doesn’t cover the initial configuration of the NAS right out of the box. What I would strongly recommend is to schedule and run the S.M.A.R.T extended test at least one time on all drives to avoid surprises about anomalies that could be found on the drives at a later time.

The first step would be to Create a Disk Group from the Storage Manager app pre-installed on the NAS. The picture below shows all drives have been mounted and initialised with a normal status


Once the wizard is concluded it is possible to review status of each drive


Next step consists in creating the first LUN (which will be served by the RAID 10 in my case). This can be accomplished by visiting the iSCSI LUN menu and click on Create. The picture below is self-explanatory and what I like is the option to already include the creation of the iSCSI Target which will be associated to the same LUN. ISCSI Targets can also be created and mapped to available LUNs separately


As per picture below I will now choose the pre-created Disk Group. Although I have selected the entire space multiple Disk Groups on the same disks are supported. They can also coexist with Volumes which is a “logical way” Synology uses to represent RAID Sets


On a different note what I did notice since the beginning of the configuration is the total capacity reported from the drives hence the one available for the RAID. By using a 4x 3TB drives in RAID 10 I was expecting a full 6TB of addressable space instead of 5.45TB as per picture below


After doing my homework the actual available space of 5579 GB shown in the wizard is absolutely right! The actual value is expressed in GibiBytes and not GigaBytes. It is just a different way of calculating the data by power of 2 or 10. Luckily Google includes a quick converter to find this out!



So based on the previous logic a 4TB LUN will use roughly 3725.29 GibiBytes


As per previous setting the wizard also includes the creation of a new iSCSI Target. For security it is recommended to enable CHAP options avoiding unauthorized connections from other iSCSI Initiators on the same network


Finally it is possible to review the settings before the actual commit of the LUN with the iSCSI configuration


After the wizard completed by clicking on Edit there are mpre settings that can be configured as per screenshots below:


If the plan is to share the same LUN as Vmware Datastore between two or more Hosts then this is the right option to check


As an extra level of security it is also possible to change the option for the LUN masking. One scenario could be to let only configured Initiators created in the this list to have Read or Read/Write access removing the Read/Write as a default behaviour. This will essentially reduce the risk of unauthorised Initiators to connect to the available iSCSI Targets

This pretty much concludes a very quick article on how to create an iSCSI LUN using a Synology NAS. Next on the line another quick article about configuring VMware ESXi to available iSCSI LUNs and use them as a Datastore for our VMs.

About the author

Michele Domanico

Passionate about Virtualization, Storage, Data Availability and Software Defined Data Center technologies. The aim of Domalab.com is sharing with the Community the knowledge and experience gained with customers, industry leaders and like minded peers. Always open to constructive feedback and new challenges.


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  • I do not have the options to create the ISCSI LUN. In storage manager I have Overview, Storage, and HDD/SSD in the left column. Nothing under HDD?SSD as is pictured in your screenshots. Any idea why this may be? My device model is RS820RP+

    • Hi Dan,
      Just wondering if you have created a Volume first? Also there should be the iSCSI Manager icon on the Control Panel to manage iSCSI LUN settings. Also I’m assuming all disks are recognized correctly from the your NAS.
      Hope this helps.


      • Hi Michele,

        Thank you for your reply. After digging around a bit I found the ISCSI settings in the SAN Manager app. I think they must have moved it in a later version. I’m still getting myself familiar with this device.

      • Oh yes! Thanks for sharing, now that you mentioned I remember too! I’m currently on earlier DSM release and will update soon to latest one. Curious to check latest changes. Enjoy your Synology NAS! Thanks Michele

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