Like Fox Mulder, I wanted to believe… that using an SSD cache on an eight bay NAS would make a noticeable difference in performance.
I received the NAS shortly after it’s release and immediately installed the additional memory. I used an assortment of hard drives of various sizes that I had on hand, and replaced them throughout the year with WD RED 6TB drives. If starting again, I would use only drives of one size, the largest available at the time. The reason is that the Synology Hybrid RAID (SHR) appears to create a RAID on top of RAIDs that span the common regions of the disks. So, with two 2TB drives and 2 1TB drives, there would be a RAID two RAIDS, one using 1TB from four drives and the other using 1TB from each of the 1TB drives. The system seems to do well to expand existing RAIDS, instead of creating new ones, when expanding, either by adding a new drive or replacing an existing drive with a larger drive. However there may be some overhead to the RAID of RAID approach, or danger. Might be nothing to it, but I’d rather have a less complex setup, one RAID of disks of all the same size.
The configuration of the NAS consists of seven WD RED 6TB HDs and one xxxx SSD. The main volume spans the seven HDs and uses Synology Hybrid RAID (SHR) with two drives of redundancy. Even with the redunancy, when streaming a large file, the HDs are likely to outperform the SSD. However, the SSD will have superior access time.
While the network configuration prevents seeing the full potential of the NAS, the hit rate statistics reported by DSM are not encouraging.