Expanding RAID 1 pool size on Synology NAS by adding more disks

I just received my first Synology NAS (so far I have used asustor) and decided to set it up. Since so far I got only two disks 18TB each I am sure will be enough for now. The idea was to configure them in Synology Hybrid RAID (SHR) and to add more to the same pool when needed.

First I want to say that the 18TB drives are still not officially supported by Synology, but I saw some websites selling the same model I got (DS1621xs+) bundled with 18TB disks, so I assumed it should work.

Well, it was a good idea to have the SHR configured, but I should of checked earlier that it is not supported on all models. And I am a little confused on the reasoning not to include it in this model. It is a high-end NAS, as Synology describes it, so it is not a hardware issue. Checking the list of models that doesn’t support it I see a lot of high-end models. May be the idea is in this class range people should use standard RAID configurations.

Why I want to expand the pool and not add a new one? The NAS has 6 slots and I will be using just 2 for now. The answer is that I want to utilize the M2 SSD cache and it can be assigned to one pool from what I see so far.

Anyways – I cannot use it. So I read a little bit more and it seems I can switch from RAID 1 to RAID 5 if I want without loosing any data. Hooray! Let’s try it before fill the disks and realize this is not possible. I have 4 spare 1TB drives that will be part of the experiment.

Let’s create the new storage pool

Out of the 4 available disks I have

will add two and will leave two for expansion.

Since this is just for tests I will “Skip drive check”, but strongly recommend to select “Perform drive check” when you do a real settup.

Click “Apply” to create it

Of course we get a warning that the drive will be erased. Click “OK”.

And the new pool is created!

We are done with the first phase. It is time to add more drives and change to RAID5 in order to do that!

Click on the 3 dots in the upper right corner of the pool and select “Change RAID Type”.

And we have two options – “Add mirror drives to RAID 1” or “RAID 5”.

Adding more drives to RAID 1 is going to increase the fault tolerance and not going to increase the disk space and we need more disk space, so we select “RAID 5”.

In the list I can see the two extra disk I have and can add them to the RAID 5.

Once they are in we can see the new estimated capacity. It went up from a little bellow 1TB to 2.7TB.

Confirming the settings again.

The data on the newly added drives will be erased. So let’s confirm.

And now we have RAID 5 with 4 disks starting from RAID 1 with 2 disks. This is very good feature! Storage manager is showing that there is an changing RAID type operation in progress and estimate how long it will take. I don’t have any real data in there, but guess this will not change the time much. It really depends if they keep information what blocks are really used or they just assume all the date need to be redistributed. My suspicion is that if there is a heavy IO going on this will affect more the time for the operation to complete.