Does anyone know the size of the non-SMR data area on the disk? I assume that's the size of a sequential write before the performance drops to a halt while writing all that to SMR. Also, random writes would perform much worse if they require multiple SMR blocks to be read and rewritten each time the non-SMR area fills up.

Perhaps a good analog for an SMR drive would be some of the early hierarchical storage servers that served data from RAM, then from spinning metal, and then from either tape or optical disks, each being slower than the previous. You could get fast writes until the RAM was full, then slower, disk-like writes while the HDs were getting filled, then excruciatingly slow throughput when you needed to hit the MO drives with little RAM or disk storage to help you.