I’ve been trying to decide between putting 16 300GB disks into a server, or 8 600GB disks. The cost of the former is a little more, but those extra spindles result in double the IOPS. I was wondering if the cost of powering them would influence me.
A quick Google indicates that SFF SAS disks consume about 39kWh per year when idle, and a little more when busy. So let’s call it 45kWh. Electricity is currently around 12 pence per kWh. So that works out at £5.40 per year per disk. So an extra eight disks in my bigger array would cost an extra £43.20 per year, or around £250 over the six year life-cycle of the server. This is not enough to influence me either way.
The other issue with lots of spindles is that it increases the probability that your RAID 10 array will fail as a result of two mirrored disks failing at the same time.