So which gives more TB per watt of power consumption?
I appreciate that you also have to factor in initial costs as large capacity drives in 2.5" format are more expensive and harder to get hold of.
The enclosures seem to be about the same cost either way.
I have 2 Dell Compellent SFF disk shelves already but I got a deal on some 2.5" disks.
Assuming only the HDDs are drawing power and the enclosure psu has 100% efficiency we can sum up idle power useage for say a 24xLFF and 24xSFF enclosure.
Max SFF disk I know is ST5000LM000 with 5TB and draws 1.8W in active idle.
24x 1.8W = 43W, 24x 5TB = 120TB, → 43W / 120TB = 0.35W/TB
Good LFF disk I know is ST16000NM001G with 16TB and draws 6.3W in active idle.
24x 6.3W = 151.2W, 24x 16TB = 384TB, → 151.2W / 384TB = 0.39W/TB
So it seems that if you only compare hdd power draw there is not much difference.
The mentined SFF disks are almost the same €/TB as the big LFF disk here in my country.
The SFF disk are no 24/7 HDDs and does use SMR tech instead of CMR.
If you buy non 24/7 LFF disks you’ll save some money as €/TB are lower than 24/7 models.
So I would choose the LFF variant as this is the more robust technoligy.
.04 W /TB May look like a small amount, but that’s more than a 10% difference, hardly negligible. I’d still go with the LFF drives for a variety of reason mostly density and robustness.