4 ms·

How do you figure? Surely SSD drives have lower power consumption than a bunch of spinning platters, even when considering the increased number you need.

wmf 16y ago
For equal capacity, they surely don't. Compare, say ten 200GB SSDs against one 2TB HDD; the power ought to be comparable (of course, the SSDs would provide dramatically higher performance).
- wtallis 16y ago
  If you're only pushing data into an SSD array at hard drive speeds, you won't be able to get all of them to stay out of idle mode, so the total power consumption of the SSD array will probably never top that of the hard drive. To bring some real-world numbers in to this, a Western Digital VelociRaptor (10K RPM) draws 6.2W while reading or writing, and 4.3W while idle but online. An Intel X25-E 64GB draws 2.6W while reading and writing, and 0.06W while idle. Let's assume that you have 7 of the SSDs in a non-RAID aggregated volume, and one of the 450GB VelociRaptors, and you're streaming data to and from them at the fastest rate the VelociRaptor can handle. In order for the SSD array to draw as much power as the active VelociRaptor, you have to average 2.3 SSDs active at once. If the transfers are mostly sequential, you will basically never have more than two SSDs active at once. If you have random accesses, then you can obviously get many of the SSDs active at once, but they can all fulfill their requests and return to idle before the VelociRaptor has served the first request. In order for your SSD array to average the same power consumption as the VelociRaptor, it would have to be executing about 7.7K random 4KB writes per second, or 83K random 4KB reads per second. That difference in performance is big enough that the power draw of SSDs will never be a net disadvantage, and the running cost of an SSD-based solution will not be higher than the running cost of a hard-drive based solution.
  - reitzensteinm 16y ago
    You're not taking the increase in the number of servers into account. Seven times as many hard drives requires seven times as many servers[1], and those extra CPUs and power supplies and cooling fans and motherboards and the extra RAM will consume far more than any power savings SSDs may give. [1]I was talking in the grandparent post about optimising for online gigabytes per watt. I'm assuming we still are, because SSDs are a huge win except for this instance. If we're talking about performance, SSDs are so much better than mechanical there's basically no comparison. Optimising for online gigabytes per watt, your servers will have the maximum number of hard drives installed, always.

wmf 16y ago

For equal capacity, they surely don't. Compare, say ten 200GB SSDs against one 2TB HDD; the power ought to be comparable (of course, the SSDs would provide dramatically higher performance).

wtallis 16y ago
If you're only pushing data into an SSD array at hard drive speeds, you won't be able to get all of them to stay out of idle mode, so the total power consumption of the SSD array will probably never top that of the hard drive. To bring some real-world numbers in to this, a Western Digital VelociRaptor (10K RPM) draws 6.2W while reading or writing, and 4.3W while idle but online. An Intel X25-E 64GB draws 2.6W while reading and writing, and 0.06W while idle. Let's assume that you have 7 of the SSDs in a non-RAID aggregated volume, and one of the 450GB VelociRaptors, and you're streaming data to and from them at the fastest rate the VelociRaptor can handle. In order for the SSD array to draw as much power as the active VelociRaptor, you have to average 2.3 SSDs active at once. If the transfers are mostly sequential, you will basically never have more than two SSDs active at once. If you have random accesses, then you can obviously get many of the SSDs active at once, but they can all fulfill their requests and return to idle before the VelociRaptor has served the first request. In order for your SSD array to average the same power consumption as the VelociRaptor, it would have to be executing about 7.7K random 4KB writes per second, or 83K random 4KB reads per second. That difference in performance is big enough that the power draw of SSDs will never be a net disadvantage, and the running cost of an SSD-based solution will not be higher than the running cost of a hard-drive based solution.
- reitzensteinm 16y ago
  You're not taking the increase in the number of servers into account. Seven times as many hard drives requires seven times as many servers[1], and those extra CPUs and power supplies and cooling fans and motherboards and the extra RAM will consume far more than any power savings SSDs may give. [1]I was talking in the grandparent post about optimising for online gigabytes per watt. I'm assuming we still are, because SSDs are a huge win except for this instance. If we're talking about performance, SSDs are so much better than mechanical there's basically no comparison. Optimising for online gigabytes per watt, your servers will have the maximum number of hard drives installed, always.