well, all you are saving vs. disks that are always active is what, 10 or 15 watts per disk? (we are talking low-power disks, I imagine) I mean, a watt-month isn't free, but even at my scale, you are looking at about $0.19 per watt for just power, $0.27 per watt month for power and rack space inclusive. I'm still small enough that I rent racks from other people, so that number is for the watt of power my equipment uses /and/ the watts the cooling system needs to burn to get rid of the waste heat from that watt.)
I wonder if simply using the backblaze type setup with 'green' drives that are set to 'power down' when not in use
would be the best solution? In that case, you'd want to minimize writes as much as reads, but it would make some sense to offer a discount for data that 'just sits there'
On the other hand, I bet that when you buy power 'at scale' you can get your watt-month prices quite a bit below $0.27 (note, you must roll in the cost of both the watt your equipment uses /and/ the watts the a/c system uses to deal with the watt of heat. At the low end, the provider bundles those two, but if you build your own data centre, you need to be careful to build that into your cost assumptions.)
The other problem with doing this at the low end is that where I am, I pay full price for a circuit, no matter how much power I pull off it (the circuit just blows if I get too carried away) and even places that do rent you metered power usually have high costs for rackspace that are not metered, so really, you are only potentially saving two or three bucks a month per disk, even if they were idle all month.
Now, also, 'green' disks are usually really slow. 5900rpm rather than 7200rpm. But they are also really cheap, so if your customers want to accept slow, you can save quite a lot on your CapEx. Like probably half, if you use consumer-grade 'green' drives rather than the 'enterprise sata' I use. Using consumer grade drives has a bunch of other problems that your software will need to account for, too... but that's a place where you potentially could have pretty big savings.
I wonder if simply using the backblaze type setup with 'green' drives that are set to 'power down' when not in use would be the best solution? In that case, you'd want to minimize writes as much as reads, but it would make some sense to offer a discount for data that 'just sits there'
On the other hand, I bet that when you buy power 'at scale' you can get your watt-month prices quite a bit below $0.27 (note, you must roll in the cost of both the watt your equipment uses /and/ the watts the a/c system uses to deal with the watt of heat. At the low end, the provider bundles those two, but if you build your own data centre, you need to be careful to build that into your cost assumptions.)
The other problem with doing this at the low end is that where I am, I pay full price for a circuit, no matter how much power I pull off it (the circuit just blows if I get too carried away) and even places that do rent you metered power usually have high costs for rackspace that are not metered, so really, you are only potentially saving two or three bucks a month per disk, even if they were idle all month.
Now, also, 'green' disks are usually really slow. 5900rpm rather than 7200rpm. But they are also really cheap, so if your customers want to accept slow, you can save quite a lot on your CapEx. Like probably half, if you use consumer-grade 'green' drives rather than the 'enterprise sata' I use. Using consumer grade drives has a bunch of other problems that your software will need to account for, too... but that's a place where you potentially could have pretty big savings.