Replacing SHR drive after "System Partition Failed"

I have a DS420 with SHR1 and 2x4TB HDDs.

Drive 2 on this Storage Pool shows this warning now and I am unsure how to proceed.

I have 2 new 10TB that I want to add to the pool and I also have a replacement 4TB.

The current 2x4TB are 80% of their capacity.

With only 4 Bays I can't do everything at once here so how exactly do I go about doing this smoothly?

It honestly made me quite anxious even though it was completely expected to happen sometime. Appreciate any response!