Thank you for your reply.
I am very clear that I want data security and I need an answer as to whether my drives are reliable or not, in this configuration. Yes, I am panicking because I have read worrying reports that my drives might fail to rebuild following a fault in one of them, and I have not heard or seen any comment to support any confidence in WD Red drives for NAS. You will know that RAID is used to guard against drive failure, and a drive that fails to recover only in that situation is a little bizarre. The fact that my data is in the home environment makes it no less important. It is, in fact, more important for me.
The DS416 has only two WD Red drives configured in RAID 1, chosen and configured for data security. The system was built and sold to me by a computer business with the intention of protecting my data. My request for this might be considered unusual for a home user. The idea is that if a drive fails it can be rebuilt and I do not lose data. The drives are not JBOD. The data is personal and important. Yes, there is some internet content. It contains a working lifetime of carefully filed information, and WD discs were trusted to look after it. (1.) above suggests that I might lose data with these drives if they are SMR drives. Thank you for the comment about the disk lifetime.
In the event of no satisfactory information about the build of these drives I will have to replace them with a make that is definitely not SMR, if I can find that knowledge. It is wrong that the customer is not given information and WD is damaged as a result.
I will follow the link to the SynoForum, although this is clearly a WD issue. I have read and understand why and when SMR is useful, but there is no justification at putting my data at risk because the company is benefiting others at my expense and is unable to answer my question. All I need to know is whether these particular drives are SMR or CMR, not too hard for a manufacturer, normally, I guess? Or the company could just say, sorry, we made the change randomly and didn’t make a note of when.
Thank you for your guidance.