Just finished a seven day cache advisor analysis. It recommends a read-write cache, but since I don’t have a UPS, I wonder if this result indicates anything about the utility of installing a read-only cache?
Are you asking if you need a UPS to have a R/W cache?
You don’t NEED one, I have one on every piece of IT hardware though. Even a cheap one to protect against brownouts and short 1 min blackouts can do wonders. I strongly recommend getting one and if you can afford it, one with USB so it can plug into the Synology and you can have them talk and have the Synology shutdown the drives when the UPS reaches x% remaining.
But here is a lot more info on Synology and SSD Caching: https://kb.synology.com/en-ph/DSM/tutorial/What_are_Some_Considerations_for_Creating_SSD_Cache