Thursday, September 03, 2015

Synology SSD Disk Cache


Subtitle: What a Palava!

I thought I would write up the process of setting up a SSD Disk Cache on a Synology NAS Network Attached Storage.


I am using a relatively old DS1812+ machine. From the last 2 digits you can see it's a 2012 generation model.


Anyway it does have 8 disk bay slots and since I upgraded to 4TB drives, well it has some free bays.  So I thought I would use some of them for a SSD cache.


Synology NAS does not have any special slot for cache, you simply use a disk bay and insert a SSD disk.


In fact you can have a read only cache with 1 SSD disk, or if you have 2 identical SSD disks, a read-write cache.


Identical Disks





First attempts went badly since I had missed the memo on the disks being identical.   WTF?  Why is this a blinking requirement.  I just don't understand.



Try Again

After a ludicrous amount of disk shuffling I managed to liberate 2 identical SSD disks.  (Non trivial as I has to clone OS off an identical second SSD disk, and that was troublesome).

Anyway








Some notes on the Synology Cache

- You need 2 identical disks, I learnt the hard way

- It's been working fine now for 2 months or so



- Initially I had an issue when one disk just disappeared.  I did the only thing a self respecting systems guy would do.   Update the SSD Disk firmware!


- The cache is now down to 32GB only sitting on 2 x 128 GB disks.  Why? Because it needs RAM memory to help with the caching and my DS1812+ has a relatively small amount of memory, so I can't afford to use the 128GB SSD as a 128GB cache.  Pretty annoying right!


- There is a cache advisor which looks at statistics and makes recommendations.


- Personally I've not noticed any performance improvements, but I just hope that there is small benefit I did not notice, and logically that actual physical disk read and writes are now reduced.


Overall it was just about worth it!  I think a more modern NAS design would allow for much larger memory capacity. Synology continues not to allow this or design for this.  (Compared to the other only sensible NAS manufacturer QNAP, which does support and allow large memory models ie. easily upto 16GB RAM).