hello 80401230
if you need data regularly, the access will be faster because the data is read from the ssd-cache. but probably only makes a difference with heavily used nas. with one ssd you can set up a read-cache. with two ssd's a read/write-cache. on the syno-homepage everything is well described.
greetings rené
ps i tested your mentioned ssd from samsung in a smaller size. works fine.

Hi

You should consider a few "restrictions" (some make sense, others less so):

1) one SSD = read-only cache possible, two SSDs (Raid-1) = read-write cache possible.
2) the cache cannot be partitioned and can only be added to a "device". So you cannot give the cache to "volume1" and an iSCSI block device. You can use only part of the SSD cache, but the rest is then unfortunately no longer usable. Unless you take two SSDs and use them only as read-only cache.
3) The larger the SSD cache, the more memory is needed (approx. 416 KB memory per 1GB SSD cache).
4) Sequential I/O can be ignored, i.e. does not run via the cache (also makes no sense, e.g. for streaming).
5) The SSD cache (at least for read-write) is part of the "device", i.e. it cannot simply be removed again but must be communicated to the system so that the data is written to the normal disks. Otherwise there will be data loss.

On the Synology page you can check which SSDs are officially supported, I assume that in general you should have no problems with NVMe SSDs, but if you want to be on the safe side, take supported SSDs.

In my opinion, it makes sense to use SSDs if you use the NAS as iSCSI storage for VMs, for example. Or if many users store their documents on it.
It makes little sense if the NAS is mainly used for audio/video/photo storage.