The 2TB unit appears to be the sweet-spot, having a lower power consumption and a lower spindle speed than the 1TB unit (for reasons unspecified in the datasheet), but 21dB vs 19dB. And it's £25/TB as opposed to £40/TB. The quoted duty cycle is 180TB/year, which is (by my reckoning) exactly what it needs to be for 24/7 buffering!
Power consumption appears to be driven by whether the unit uses CMR or SMR, and the S300 range comprises 1, 2, 4, & 6TB models in a mixture of CMR and SMR technologies, with some capacities available in both (both the
Toshiba web page and
datasheet are garbled, containing typos and no clarification why there are
three models with 4TB capacity!).
Thinking SMR might stand for Super Magneto Resistive (a recording head technology) and wondering what CMR might be, I went looking and discovered SMR isn't that at all: apparently it's Conventional Magnetic Recording vs Shingled Magnetic Recording, the latter allowing tracks to actually overlap and therefore pack more onto a platter. So there's less moving mass per TB with SMR, hence the lower power consumption, but still no explanation why the 1TB unit spins at 5700rpm vs 5400rpm for all the other units.
Is SMR a good or a bad thing? Well, according to
this article SMR requires writes to be cached to a CMR section of the drive for an intricate dance involving writing multiple tracks on the SMR section, and (I extrapolate) might be what gave the WD Red series a bad name. The problem is if the cache fills up, so writes are then forced to go directly to SMR in which case the write speed reduces dramatically.
Nonetheless, Toshiba rate these drives as recording from 64 HiDef sources simultaneously, so they don't think the sustained write performance is a problem.
Conclusion: maybe settle for the 1TB CMR unit. Or be a pioneer and experiment with the 2TB SMR unit in the interests of science.