Adding an SSD cache to Synology DS-1813+

Hello everyone,

I bought – some time ago, new storage for my home lab.  I mentioned it here, but while I got it going quickly I have been very slow at getting the SSD’s I had bought into action.  I had some time recently and it was a little different so I thought I would document and share.

Lets get started.

Before you start

Somethings to think about before we get started.

  • Make sure the SSD is on the Synology Hardware Compatibility List.
  • You need to use two SSD of the same size, brand, and model.
  • You need to add additional memory – I added 2048 GB.  With that I have a total of 4 GB of system memory and that will allow me to use up to about 223 GB of cache.
  • Some nice background on Cache in Synology including some test results can be found in this.  It was this technical white paper that showed me clearly that Read write cache is the way to go.
  • FYI I am using in this a Synology DS1813+ which I am very happy with.


Check out this picture after unpacking (as always you can click on the pictures or screenshots to see a bigger image).


BTW, the SSD I purchased was Intel SSD 530 Series 240 GB dries.  I shopped between the Synology SSD compatibility list and Amazon until I found something reasonable priced.

Something not in the picture is the little bag of screws that came with the NAS as well as screwdrivers – which you can see below.


You need to screw the SSD into the two trays.  There is only one way to do that which will end up with the connectors in the right place.  It worked better for me to remove one of the connector rails.


As I mentioned above the connector on the right side of the enclosure seen above is not connected.  So you will have two leftovers as seen below when you are done.  Notice above how much of the drive connector is visible?


These should be familiar to you as they are part of the very interesting way to secure the hard disks into the enclosure.

Now that the two enclosures have the SSD installed you should insert them into the NAS.  Once installed, above the new drives you should see a brief green light.

Working in the UI – do we see the SSD?

We need to make sure the drives are seen properly.  You should have the Storage Manager on your Synology desktop.  Open it up and change to the HDD/SSD view.  BTW, if you don’t see the Storage Manager you can add that to your desktop from the apps using the icon in the top left corner.


We can see at the bottom of the list of drives our two new SSD.  And both are reported properly in terms of size too.  So now we move on to working with our cache.

Creating a Cache

Now in the same interface we change to the SSD Cache view.


It is telling us there is no SSD cache.  Surprise.

  • Use the Create button to start.  It will open a wizard.


  • I think it is best to use the Read-write cache if you can.


  • Now we can select our disks, as you can see I did above.
  • We also need to select what mount point for the SSD cache.


  • You can see above Volume 1 which is what I am attaching this SSD Cache too.  I am a new person to Synology and I used Volume 1 for both CIFS and NFS which may have been a poor decision.  I think maybe two volumes – one for CIFS and one for NFS may have been better as I could have attached the cache to only the NFS share which is where I have my VMs and what I need cached.  But then I would have had to manage space and not sure if I want to do that.
  • In the next screen we see what the Cache size is going to be.  There is a formula that includes memory and I think RAID as well and it ends up in providing you with the max cache size.  In my case it is 223 GB.


  • Now we have to confirm that we know the SSD are going to be erased.


  • After we agree things happen.



  • We end up needing to log in again.  Not sure if that is because I took so long doing this and it was a time log out or something to do with the creation of the Cache.  But once I logged in again and return to the SSD Cache I see our new cache.


  • If you use the drop down arrow to expand what we see above you get the info below.


  • We see a lot of good info on the Cache.  The important things are capacity and hit ratio.  But also interesting to see how much RAM this cache uses.
  • If you use the File Access Statistics button you will see below what you get.


  • This will be way more interesting in the future I suspect.


You should now have SSD installed, with a Cache created, and attached to a volume.  You may have it attached to an iSCSI LUN or you may have it attached to a different volume then I did.

Questions or comment, just let me know.


=== END ===


17 thoughts on “Adding an SSD cache to Synology DS-1813+

  1. I have an 1812+ and created a straight 256gb x4 iSCSI array with SSDs. We will have to compare notes on performance numbers between the two. I am curious to see difference.


    1. Let me know how you plan to measure, and I will use same. Better numbers to compare that way. But interesting due to NFS / iSCSI thing. I have started to move everything to NFS to avoid things like UNMAP and make things easier.


    1. I have not had time to measure yet, but anecdotally I see no improvement. I need to play with it as I think it should have some improvement. The vendor sure suggests it should.

    1. Tough question really. No easy answer. But Iometer is a very common tool. Process is important though. This might help too. Sorry not more help but it is not my thing, and I have not done much of this. I need to though!


  2. I’m installed 2 ssd almost identical of your setup, used and test about 2 weeks, I don’t see any data transfer or any performance and speed improvement, may be a little slower than without using ssd cache. I just feel it’s kind of waste 2 bay. little be disappointed. I think synology should work improve this.

    How about yours, if you have any update, please post and share.

  3. Could you tell me which one is better between 2 options:
    1. Deploy SSD Cache with 1 * 256GB SSD
    2. Deploy SSD Cache with 2 * 128GB SSD

    And why?

    Thank you.

    1. If you want to do cache, you need two. If you are going to treat them as disk, I could see a case for two as long term that might mean if there is an issue only one will be impacted. But personally, I would go with the 1 256 as it is eaier to manage and I like more storage capacity.


  4. You bought 2 identical 240GB SSDs for a RAID-1 read and write cache.

    During the cache configuration wizard it says “Only 1/4 of the system memory” and “the unused memory you have expanded”

    So I am thinking with my DS1813+ I added the extra 2GB memory module therefore I can use all of that 2GB for SSD caching also I can use 1/4 of the onboard 2GB = 512MB for SSD caching.

    Using the formula of 1GB of SSD needs 4MB of memory

    2.5GB = 2,560MB

    2,560MB / 4MB = 640GB maximum of SSD cache in the DS1813+

    Therefore I think adding a pair of 512GB SSDs to my DS1813+ should NOT be a waste of money and it should be able to use it all.

    512GB = 2,047MB of memory required ( since I have the 2GB expansion module its all good )

    Do you have any thoughts on my maths or understanding of the Synology implementation of SSD caching ?

    1. Hi Simon,

      I have since found a number of people that have done what I did and found no, or not much improvement, I just checked with them and they have undone their work, and are doing SSD caching, but are using the SSD as disk, and that does make a noticeable improvement. When I catch up in lab work, I will do this as well.


  5. In your article you said “With that I have a total of 4 GB of system memory and that will allow me to use up to about 223 GB of cache.” which I think is incorrect.

  6. Why do we need two (2) SSD’s? I don’t find the reason for that requirement in your article. Could you please explain it?

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